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x86/efi: Avoid triple faults during EFI mixed mode calls

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Andy pointed out that if an NMI or MCE is received while we're in the
middle of an EFI mixed mode call a triple fault will occur. This can
happen, for example, when issuing an EFI mixed mode call while running
perf.

The reason for the triple fault is that we execute the mixed mode call
in 32-bit mode with paging disabled but with 64-bit kernel IDT handlers
installed throughout the call.

At Andy's suggestion, stop playing the games we currently do at runtime,
such as disabling paging and installing a 32-bit GDT for __KERNEL_CS. We
can simply switch to the __KERNEL32_CS descriptor before invoking
firmware services, and run in compatibility mode. This way, if an
NMI/MCE does occur the kernel IDT handler will execute correctly, since
it'll jump to __KERNEL_CS automatically.

However, this change is only possible post-ExitBootServices(). Before
then the firmware "owns" the machine and expects for its 32-bit IDT
handlers to be left intact to service interrupts, etc.

So, we now need to distinguish between early boot and runtime
invocations of EFI services. During early boot, we need to restore the
GDT that the firmware expects to be present. We can only jump to the
__KERNEL32_CS code segment for mixed mode calls after ExitBootServices()
has been invoked.

A liberal sprinkling of comments in the thunking code should make the
differences in early and late environments more apparent.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Tested-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
This commit is contained in:
Matt Fleming 2015-01-13 15:25:00 +00:00
parent 3c01b74e81
commit 96738c69a7
5 changed files with 301 additions and 203 deletions
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1
arch/x86/boot/compressed/Makefile
View File

@ -49,6 +49,7 @@ $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
vmlinux-objs-$(CONFIG_EFI_STUB) += $(obj)/eboot.o $(obj)/efi_stub_$(BITS).o \
$(objtree)/drivers/firmware/efi/libstub/lib.a
vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
$(call if_changed,ld)

25
arch/x86/boot/compressed/efi_stub_64.S
View File

@ -3,28 +3,3 @@
#include <asm/processor-flags.h>
#include "../../platform/efi/efi_stub_64.S"
#ifdef CONFIG_EFI_MIXED
.code64
.text
ENTRY(efi64_thunk)
push %rbp
push %rbx
subq $16, %rsp
leaq efi_exit32(%rip), %rax
movl %eax, 8(%rsp)
leaq efi_gdt64(%rip), %rax
movl %eax, 4(%rsp)
movl %eax, 2(%rax) /* Fixup the gdt base address */
leaq efi32_boot_gdt(%rip), %rax
movl %eax, (%rsp)
call __efi64_thunk
addq $16, %rsp
pop %rbx
pop %rbp
ret
ENDPROC(efi64_thunk)
#endif /* CONFIG_EFI_MIXED */

196
arch/x86/boot/compressed/efi_thunk_64.S Normal file
View File

@ -0,0 +1,196 @@
/*
* Copyright (C) 2014, 2015 Intel Corporation; author Matt Fleming
*
* Early support for invoking 32-bit EFI services from a 64-bit kernel.
*
* Because this thunking occurs before ExitBootServices() we have to
* restore the firmware's 32-bit GDT before we make EFI serivce calls,
* since the firmware's 32-bit IDT is still currently installed and it
* needs to be able to service interrupts.
*
* On the plus side, we don't have to worry about mangling 64-bit
* addresses into 32-bits because we're executing with an identify
* mapped pagetable and haven't transitioned to 64-bit virtual addresses
* yet.
*/
#include <linux/linkage.h>
#include <asm/msr.h>
#include <asm/page_types.h>
#include <asm/processor-flags.h>
#include <asm/segment.h>
.code64
.text
ENTRY(efi64_thunk)
push %rbp
push %rbx
subq $8, %rsp
leaq efi_exit32(%rip), %rax
movl %eax, 4(%rsp)
leaq efi_gdt64(%rip), %rax
movl %eax, (%rsp)
movl %eax, 2(%rax) /* Fixup the gdt base address */
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
/*
* Convert x86-64 ABI params to i386 ABI
*/
subq $32, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
sgdt save_gdt(%rip)
leaq 1f(%rip), %rbx
movq %rbx, func_rt_ptr(%rip)
/*
* Switch to gdt with 32-bit segments. This is the firmware GDT
* that was installed when the kernel started executing. This
* pointer was saved at the EFI stub entry point in head_64.S.
*/
leaq efi32_boot_gdt(%rip), %rax
lgdt (%rax)
pushq $__KERNEL_CS
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
1: addq $32, %rsp
lgdt save_gdt(%rip)
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
addq $8, %rsp
pop %rbx
pop %rbp
ret
ENDPROC(efi64_thunk)
ENTRY(efi_exit32)
movq func_rt_ptr(%rip), %rax
push %rax
mov %rdi, %rax
ret
ENDPROC(efi_exit32)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
ENTRY(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/* Reload pgtables */
movl %cr3, %eax
movl %eax, %cr3
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Disable long mode via EFER */
movl $MSR_EFER, %ecx
rdmsr
btrl $_EFER_LME, %eax
wrmsr
call *%edi
/* We must preserve return value */
movl %eax, %edi
/*
* Some firmware will return with interrupts enabled. Be sure to
* disable them before we switch GDTs.
*/
cli
movl 56(%esp), %eax
movl %eax, 2(%eax)
lgdtl (%eax)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
movl %eax, %cr4
movl %cr3, %eax
movl %eax, %cr3
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
xorl %eax, %eax
lldt %ax
movl 60(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
lret
ENDPROC(efi_enter32)
.data
.balign 8
.global efi32_boot_gdt
efi32_boot_gdt: .word 0
.quad 0
save_gdt: .word 0
.quad 0
func_rt_ptr: .quad 0
.global efi_gdt64
efi_gdt64:
.word efi_gdt64_end - efi_gdt64
.long 0 /* Filled out by user */
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x0080890000000000 /* TS descriptor */
.quad 0x0000000000000000 /* TS continued */
efi_gdt64_end:

161
arch/x86/platform/efi/efi_stub_64.S
View File

@ -91,167 +91,6 @@ ENTRY(efi_call)
ret
ENDPROC(efi_call)
#ifdef CONFIG_EFI_MIXED
/*
* We run this function from the 1:1 mapping.
*
* This function must be invoked with a 1:1 mapped stack.
*/
ENTRY(__efi64_thunk)
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
subq $32, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
sgdt save_gdt(%rip)
leaq 1f(%rip), %rbx
movq %rbx, func_rt_ptr(%rip)
/* Switch to gdt with 32-bit segments */
movl 64(%rsp), %eax
lgdt (%rax)
leaq efi_enter32(%rip), %rax
pushq $__KERNEL_CS
pushq %rax
lretq
1: addq $32, %rsp
lgdt save_gdt(%rip)
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
ret
ENDPROC(__efi64_thunk)
ENTRY(efi_exit32)
movq func_rt_ptr(%rip), %rax
push %rax
mov %rdi, %rax
ret
ENDPROC(efi_exit32)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
ENTRY(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/* Reload pgtables */
movl %cr3, %eax
movl %eax, %cr3
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Disable long mode via EFER */
movl $MSR_EFER, %ecx
rdmsr
btrl $_EFER_LME, %eax
wrmsr
call *%edi
/* We must preserve return value */
movl %eax, %edi
/*
* Some firmware will return with interrupts enabled. Be sure to
* disable them before we switch GDTs.
*/
cli
movl 68(%esp), %eax
movl %eax, 2(%eax)
lgdtl (%eax)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
movl %eax, %cr4
movl %cr3, %eax
movl %eax, %cr3
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
xorl %eax, %eax
lldt %ax
movl 72(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
lret
ENDPROC(efi_enter32)
.data
.balign 8
.global efi32_boot_gdt
efi32_boot_gdt: .word 0
.quad 0
save_gdt: .word 0
.quad 0
func_rt_ptr: .quad 0
.global efi_gdt64
efi_gdt64:
.word efi_gdt64_end - efi_gdt64
.long 0 /* Filled out by user */
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x0080890000000000 /* TS descriptor */
.quad 0x0000000000000000 /* TS continued */
efi_gdt64_end:
#endif /* CONFIG_EFI_MIXED */
.data
ENTRY(efi_scratch)
.fill 3,8,0

121
arch/x86/platform/efi/efi_thunk_64.S
View File

@ -1,9 +1,26 @@
/*
* Copyright (C) 2014 Intel Corporation; author Matt Fleming
*
* Support for invoking 32-bit EFI runtime services from a 64-bit
* kernel.
*
* The below thunking functions are only used after ExitBootServices()
* has been called. This simplifies things considerably as compared with
* the early EFI thunking because we can leave all the kernel state
* intact (GDT, IDT, etc) and simply invoke the the 32-bit EFI runtime
* services from __KERNEL32_CS. This means we can continue to service
* interrupts across an EFI mixed mode call.
*
* We do however, need to handle the fact that we're running in a full
* 64-bit virtual address space. Things like the stack and instruction
* addresses need to be accessible by the 32-bit firmware, so we rely on
* using the identity mappings in the EFI page table to access the stack
* and kernel text (see efi_setup_page_tables()).
*/
#include <linux/linkage.h>
#include <asm/page_types.h>
#include <asm/segment.h>
.text
.code64
@ -33,14 +50,6 @@ ENTRY(efi64_thunk)
leaq efi_exit32(%rip), %rbx
subq %rax, %rbx
movl %ebx, 8(%rsp)
leaq efi_gdt64(%rip), %rbx
subq %rax, %rbx
movl %ebx, 2(%ebx)
movl %ebx, 4(%rsp)
leaq efi_gdt32(%rip), %rbx
subq %rax, %rbx
movl %ebx, 2(%ebx)
movl %ebx, (%rsp)
leaq __efi64_thunk(%rip), %rbx
subq %rax, %rbx
@ -52,14 +61,92 @@ ENTRY(efi64_thunk)
retq
ENDPROC(efi64_thunk)
.data
efi_gdt32:
.word efi_gdt32_end - efi_gdt32
.long 0 /* Filled out above */
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00cf9a000000ffff /* __KERNEL_CS */
.quad 0x00cf93000000ffff /* __KERNEL_DS */
efi_gdt32_end:
/*
* We run this function from the 1:1 mapping.
*
* This function must be invoked with a 1:1 mapped stack.
*/
ENTRY(__efi64_thunk)
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
subq $32, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
leaq 1f(%rip), %rbx
movq %rbx, func_rt_ptr(%rip)
/* Switch to 32-bit descriptor */
pushq $__KERNEL32_CS
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
1: addq $32, %rsp
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
ret
ENDPROC(__efi64_thunk)
ENTRY(efi_exit32)
movq func_rt_ptr(%rip), %rax
push %rax
mov %rdi, %rax
ret
ENDPROC(efi_exit32)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
ENTRY(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
call *%edi
/* We must preserve return value */
movl %eax, %edi
movl 72(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
lret
ENDPROC(efi_enter32)
.data
.balign 8
func_rt_ptr: .quad 0
efi_saved_sp: .quad 0