8f577cadf7
Take advantage of internal BPF JIT
05-sim-long_jumps.c of libseccomp was used as micro-benchmark:
seccomp_rule_add_exact(ctx,...
seccomp_rule_add_exact(ctx,...
rc = seccomp_load(ctx);
for (i = 0; i < 10000000; i++)
syscall(...);
$ sudo sysctl net.core.bpf_jit_enable=1
$ time ./bench
real 0m2.769s
user 0m1.136s
sys 0m1.624s
$ sudo sysctl net.core.bpf_jit_enable=0
$ time ./bench
real 0m5.825s
user 0m1.268s
sys 0m4.548s
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
523 lines
14 KiB
C
523 lines
14 KiB
C
/*
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* linux/kernel/seccomp.c
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*
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* Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com>
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*
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* Copyright (C) 2012 Google, Inc.
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* Will Drewry <wad@chromium.org>
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*
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* This defines a simple but solid secure-computing facility.
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*
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* Mode 1 uses a fixed list of allowed system calls.
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* Mode 2 allows user-defined system call filters in the form
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* of Berkeley Packet Filters/Linux Socket Filters.
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*/
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#include <linux/atomic.h>
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#include <linux/audit.h>
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#include <linux/compat.h>
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#include <linux/sched.h>
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#include <linux/seccomp.h>
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/* #define SECCOMP_DEBUG 1 */
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#ifdef CONFIG_SECCOMP_FILTER
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#include <asm/syscall.h>
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#include <linux/filter.h>
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#include <linux/ptrace.h>
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#include <linux/security.h>
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#include <linux/slab.h>
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#include <linux/tracehook.h>
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#include <linux/uaccess.h>
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/**
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* struct seccomp_filter - container for seccomp BPF programs
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*
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* @usage: reference count to manage the object lifetime.
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* get/put helpers should be used when accessing an instance
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* outside of a lifetime-guarded section. In general, this
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* is only needed for handling filters shared across tasks.
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* @prev: points to a previously installed, or inherited, filter
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* @len: the number of instructions in the program
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* @insns: the BPF program instructions to evaluate
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*
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* seccomp_filter objects are organized in a tree linked via the @prev
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* pointer. For any task, it appears to be a singly-linked list starting
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* with current->seccomp.filter, the most recently attached or inherited filter.
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* However, multiple filters may share a @prev node, by way of fork(), which
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* results in a unidirectional tree existing in memory. This is similar to
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* how namespaces work.
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*
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* seccomp_filter objects should never be modified after being attached
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* to a task_struct (other than @usage).
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*/
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struct seccomp_filter {
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atomic_t usage;
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struct seccomp_filter *prev;
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struct sk_filter *prog;
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};
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/* Limit any path through the tree to 256KB worth of instructions. */
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#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
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/*
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* Endianness is explicitly ignored and left for BPF program authors to manage
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* as per the specific architecture.
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*/
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static void populate_seccomp_data(struct seccomp_data *sd)
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{
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struct task_struct *task = current;
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struct pt_regs *regs = task_pt_regs(task);
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unsigned long args[6];
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sd->nr = syscall_get_nr(task, regs);
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sd->arch = syscall_get_arch();
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syscall_get_arguments(task, regs, 0, 6, args);
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sd->args[0] = args[0];
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sd->args[1] = args[1];
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sd->args[2] = args[2];
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sd->args[3] = args[3];
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sd->args[4] = args[4];
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sd->args[5] = args[5];
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sd->instruction_pointer = KSTK_EIP(task);
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}
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/**
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* seccomp_check_filter - verify seccomp filter code
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* @filter: filter to verify
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* @flen: length of filter
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*
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* Takes a previously checked filter (by sk_chk_filter) and
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* redirects all filter code that loads struct sk_buff data
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* and related data through seccomp_bpf_load. It also
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* enforces length and alignment checking of those loads.
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*
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* Returns 0 if the rule set is legal or -EINVAL if not.
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*/
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static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
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{
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int pc;
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for (pc = 0; pc < flen; pc++) {
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struct sock_filter *ftest = &filter[pc];
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u16 code = ftest->code;
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u32 k = ftest->k;
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switch (code) {
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case BPF_S_LD_W_ABS:
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ftest->code = BPF_LDX | BPF_W | BPF_ABS;
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/* 32-bit aligned and not out of bounds. */
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if (k >= sizeof(struct seccomp_data) || k & 3)
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return -EINVAL;
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continue;
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case BPF_S_LD_W_LEN:
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ftest->code = BPF_LD | BPF_IMM;
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ftest->k = sizeof(struct seccomp_data);
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continue;
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case BPF_S_LDX_W_LEN:
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ftest->code = BPF_LDX | BPF_IMM;
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ftest->k = sizeof(struct seccomp_data);
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continue;
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/* Explicitly include allowed calls. */
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case BPF_S_RET_K:
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case BPF_S_RET_A:
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case BPF_S_ALU_ADD_K:
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case BPF_S_ALU_ADD_X:
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case BPF_S_ALU_SUB_K:
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case BPF_S_ALU_SUB_X:
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case BPF_S_ALU_MUL_K:
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case BPF_S_ALU_MUL_X:
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case BPF_S_ALU_DIV_X:
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case BPF_S_ALU_AND_K:
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case BPF_S_ALU_AND_X:
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case BPF_S_ALU_OR_K:
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case BPF_S_ALU_OR_X:
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case BPF_S_ALU_XOR_K:
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case BPF_S_ALU_XOR_X:
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case BPF_S_ALU_LSH_K:
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case BPF_S_ALU_LSH_X:
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case BPF_S_ALU_RSH_K:
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case BPF_S_ALU_RSH_X:
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case BPF_S_ALU_NEG:
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case BPF_S_LD_IMM:
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case BPF_S_LDX_IMM:
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case BPF_S_MISC_TAX:
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case BPF_S_MISC_TXA:
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case BPF_S_ALU_DIV_K:
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case BPF_S_LD_MEM:
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case BPF_S_LDX_MEM:
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case BPF_S_ST:
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case BPF_S_STX:
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case BPF_S_JMP_JA:
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case BPF_S_JMP_JEQ_K:
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case BPF_S_JMP_JEQ_X:
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case BPF_S_JMP_JGE_K:
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case BPF_S_JMP_JGE_X:
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case BPF_S_JMP_JGT_K:
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case BPF_S_JMP_JGT_X:
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case BPF_S_JMP_JSET_K:
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case BPF_S_JMP_JSET_X:
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sk_decode_filter(ftest, ftest);
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continue;
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default:
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return -EINVAL;
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}
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}
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return 0;
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}
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/**
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* seccomp_run_filters - evaluates all seccomp filters against @syscall
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* @syscall: number of the current system call
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*
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* Returns valid seccomp BPF response codes.
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*/
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static u32 seccomp_run_filters(int syscall)
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{
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struct seccomp_filter *f;
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struct seccomp_data sd;
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u32 ret = SECCOMP_RET_ALLOW;
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/* Ensure unexpected behavior doesn't result in failing open. */
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if (WARN_ON(current->seccomp.filter == NULL))
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return SECCOMP_RET_KILL;
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populate_seccomp_data(&sd);
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/*
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* All filters in the list are evaluated and the lowest BPF return
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* value always takes priority (ignoring the DATA).
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*/
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for (f = current->seccomp.filter; f; f = f->prev) {
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u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
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if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
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ret = cur_ret;
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}
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return ret;
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}
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/**
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* seccomp_attach_filter: Attaches a seccomp filter to current.
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* @fprog: BPF program to install
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*
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* Returns 0 on success or an errno on failure.
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*/
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static long seccomp_attach_filter(struct sock_fprog *fprog)
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{
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struct seccomp_filter *filter;
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unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
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unsigned long total_insns = fprog->len;
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struct sock_filter *fp;
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int new_len;
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long ret;
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if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
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return -EINVAL;
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for (filter = current->seccomp.filter; filter; filter = filter->prev)
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total_insns += filter->prog->len + 4; /* include a 4 instr penalty */
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if (total_insns > MAX_INSNS_PER_PATH)
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return -ENOMEM;
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/*
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* Installing a seccomp filter requires that the task have
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* CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
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* This avoids scenarios where unprivileged tasks can affect the
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* behavior of privileged children.
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*/
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if (!current->no_new_privs &&
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security_capable_noaudit(current_cred(), current_user_ns(),
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CAP_SYS_ADMIN) != 0)
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return -EACCES;
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fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
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if (!fp)
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return -ENOMEM;
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/* Copy the instructions from fprog. */
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ret = -EFAULT;
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if (copy_from_user(fp, fprog->filter, fp_size))
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goto free_prog;
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/* Check and rewrite the fprog via the skb checker */
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ret = sk_chk_filter(fp, fprog->len);
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if (ret)
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goto free_prog;
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/* Check and rewrite the fprog for seccomp use */
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ret = seccomp_check_filter(fp, fprog->len);
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if (ret)
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goto free_prog;
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/* Convert 'sock_filter' insns to 'sock_filter_int' insns */
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ret = sk_convert_filter(fp, fprog->len, NULL, &new_len);
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if (ret)
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goto free_prog;
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/* Allocate a new seccomp_filter */
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ret = -ENOMEM;
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filter = kzalloc(sizeof(struct seccomp_filter),
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GFP_KERNEL|__GFP_NOWARN);
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if (!filter)
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goto free_prog;
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filter->prog = kzalloc(sk_filter_size(new_len),
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GFP_KERNEL|__GFP_NOWARN);
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if (!filter->prog)
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goto free_filter;
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ret = sk_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len);
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if (ret)
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goto free_filter_prog;
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kfree(fp);
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atomic_set(&filter->usage, 1);
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filter->prog->len = new_len;
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filter->prog->bpf_func = (void *)sk_run_filter_int_seccomp;
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/* JIT internal BPF into native HW instructions */
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bpf_int_jit_compile(filter->prog);
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/*
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* If there is an existing filter, make it the prev and don't drop its
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* task reference.
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*/
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filter->prev = current->seccomp.filter;
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current->seccomp.filter = filter;
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return 0;
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free_filter_prog:
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kfree(filter->prog);
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free_filter:
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kfree(filter);
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free_prog:
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kfree(fp);
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return ret;
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}
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/**
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* seccomp_attach_user_filter - attaches a user-supplied sock_fprog
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* @user_filter: pointer to the user data containing a sock_fprog.
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*
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* Returns 0 on success and non-zero otherwise.
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*/
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static long seccomp_attach_user_filter(char __user *user_filter)
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{
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struct sock_fprog fprog;
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long ret = -EFAULT;
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#ifdef CONFIG_COMPAT
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if (is_compat_task()) {
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struct compat_sock_fprog fprog32;
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if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
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goto out;
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fprog.len = fprog32.len;
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fprog.filter = compat_ptr(fprog32.filter);
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} else /* falls through to the if below. */
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#endif
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if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
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goto out;
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ret = seccomp_attach_filter(&fprog);
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out:
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return ret;
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}
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/* get_seccomp_filter - increments the reference count of the filter on @tsk */
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void get_seccomp_filter(struct task_struct *tsk)
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{
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struct seccomp_filter *orig = tsk->seccomp.filter;
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if (!orig)
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return;
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/* Reference count is bounded by the number of total processes. */
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atomic_inc(&orig->usage);
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}
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/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
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void put_seccomp_filter(struct task_struct *tsk)
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{
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struct seccomp_filter *orig = tsk->seccomp.filter;
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/* Clean up single-reference branches iteratively. */
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while (orig && atomic_dec_and_test(&orig->usage)) {
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struct seccomp_filter *freeme = orig;
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orig = orig->prev;
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bpf_jit_free(freeme->prog);
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kfree(freeme);
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}
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}
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/**
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* seccomp_send_sigsys - signals the task to allow in-process syscall emulation
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* @syscall: syscall number to send to userland
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* @reason: filter-supplied reason code to send to userland (via si_errno)
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*
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* Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
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*/
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static void seccomp_send_sigsys(int syscall, int reason)
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{
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struct siginfo info;
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memset(&info, 0, sizeof(info));
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info.si_signo = SIGSYS;
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info.si_code = SYS_SECCOMP;
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info.si_call_addr = (void __user *)KSTK_EIP(current);
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info.si_errno = reason;
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info.si_arch = syscall_get_arch();
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info.si_syscall = syscall;
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force_sig_info(SIGSYS, &info, current);
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}
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#endif /* CONFIG_SECCOMP_FILTER */
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/*
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* Secure computing mode 1 allows only read/write/exit/sigreturn.
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* To be fully secure this must be combined with rlimit
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* to limit the stack allocations too.
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*/
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static int mode1_syscalls[] = {
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__NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
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0, /* null terminated */
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};
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#ifdef CONFIG_COMPAT
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static int mode1_syscalls_32[] = {
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__NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
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0, /* null terminated */
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};
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#endif
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int __secure_computing(int this_syscall)
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{
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int mode = current->seccomp.mode;
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int exit_sig = 0;
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int *syscall;
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u32 ret;
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switch (mode) {
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case SECCOMP_MODE_STRICT:
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syscall = mode1_syscalls;
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#ifdef CONFIG_COMPAT
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if (is_compat_task())
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syscall = mode1_syscalls_32;
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#endif
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do {
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if (*syscall == this_syscall)
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return 0;
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} while (*++syscall);
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exit_sig = SIGKILL;
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ret = SECCOMP_RET_KILL;
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break;
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#ifdef CONFIG_SECCOMP_FILTER
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case SECCOMP_MODE_FILTER: {
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int data;
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struct pt_regs *regs = task_pt_regs(current);
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ret = seccomp_run_filters(this_syscall);
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data = ret & SECCOMP_RET_DATA;
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ret &= SECCOMP_RET_ACTION;
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switch (ret) {
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case SECCOMP_RET_ERRNO:
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/* Set the low-order 16-bits as a errno. */
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syscall_set_return_value(current, regs,
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-data, 0);
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goto skip;
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case SECCOMP_RET_TRAP:
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/* Show the handler the original registers. */
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syscall_rollback(current, regs);
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/* Let the filter pass back 16 bits of data. */
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seccomp_send_sigsys(this_syscall, data);
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goto skip;
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case SECCOMP_RET_TRACE:
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/* Skip these calls if there is no tracer. */
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if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
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syscall_set_return_value(current, regs,
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-ENOSYS, 0);
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goto skip;
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}
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/* Allow the BPF to provide the event message */
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ptrace_event(PTRACE_EVENT_SECCOMP, data);
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/*
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* The delivery of a fatal signal during event
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* notification may silently skip tracer notification.
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* Terminating the task now avoids executing a system
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* call that may not be intended.
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*/
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if (fatal_signal_pending(current))
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break;
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if (syscall_get_nr(current, regs) < 0)
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goto skip; /* Explicit request to skip. */
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return 0;
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case SECCOMP_RET_ALLOW:
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return 0;
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case SECCOMP_RET_KILL:
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default:
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break;
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}
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exit_sig = SIGSYS;
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break;
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}
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#endif
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default:
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BUG();
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}
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#ifdef SECCOMP_DEBUG
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dump_stack();
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#endif
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audit_seccomp(this_syscall, exit_sig, ret);
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do_exit(exit_sig);
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#ifdef CONFIG_SECCOMP_FILTER
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skip:
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audit_seccomp(this_syscall, exit_sig, ret);
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#endif
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return -1;
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}
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long prctl_get_seccomp(void)
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{
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return current->seccomp.mode;
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}
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/**
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* prctl_set_seccomp: configures current->seccomp.mode
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* @seccomp_mode: requested mode to use
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* @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
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*
|
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* This function may be called repeatedly with a @seccomp_mode of
|
|
* SECCOMP_MODE_FILTER to install additional filters. Every filter
|
|
* successfully installed will be evaluated (in reverse order) for each system
|
|
* call the task makes.
|
|
*
|
|
* Once current->seccomp.mode is non-zero, it may not be changed.
|
|
*
|
|
* Returns 0 on success or -EINVAL on failure.
|
|
*/
|
|
long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
|
|
{
|
|
long ret = -EINVAL;
|
|
|
|
if (current->seccomp.mode &&
|
|
current->seccomp.mode != seccomp_mode)
|
|
goto out;
|
|
|
|
switch (seccomp_mode) {
|
|
case SECCOMP_MODE_STRICT:
|
|
ret = 0;
|
|
#ifdef TIF_NOTSC
|
|
disable_TSC();
|
|
#endif
|
|
break;
|
|
#ifdef CONFIG_SECCOMP_FILTER
|
|
case SECCOMP_MODE_FILTER:
|
|
ret = seccomp_attach_user_filter(filter);
|
|
if (ret)
|
|
goto out;
|
|
break;
|
|
#endif
|
|
default:
|
|
goto out;
|
|
}
|
|
|
|
current->seccomp.mode = seccomp_mode;
|
|
set_thread_flag(TIF_SECCOMP);
|
|
out:
|
|
return ret;
|
|
}
|