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objtool: Add Direction Flag validation

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Having DF escape is BAD(tm).

Linus; you suggested this one, but since DF really is only used from
ASM and the failure case is fairly obvious, do we really need this?

OTOH the patch is fairly small and simple, so let's just do this
to demonstrate objtool's superior awesomeness.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-02-25 11:10:55 +01:00 committed by Ingo Molnar
parent ea24213d80
commit 2f0f9e9ad7
4 changed files with 37 additions and 2 deletions
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4
tools/objtool/arch.h
View File

@ -35,7 +35,9 @@
#define INSN_NOP 10
#define INSN_STAC 11
#define INSN_CLAC 12
#define INSN_OTHER 13
#define INSN_STD 13
#define INSN_CLD 14
#define INSN_OTHER 15
#define INSN_LAST INSN_OTHER
enum op_dest_type {

8
tools/objtool/arch/x86/decode.c
View File

@ -451,6 +451,14 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
*type = INSN_CALL;
break;
case 0xfc:
*type = INSN_CLD;
break;
case 0xfd:
*type = INSN_STD;
break;
case 0xff:
if (modrm_reg == 2 || modrm_reg == 3)

25
tools/objtool/check.c
View File

@ -1903,6 +1903,12 @@ static int validate_call(struct instruction *insn, struct insn_state *state)
return 1;
}
if (state->df) {
WARN_FUNC("call to %s() with DF set",
insn->sec, insn->offset, insn_dest_name(insn));
return 1;
}
return 0;
}
@ -2044,6 +2050,11 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
return 1;
}
if (state.df) {
WARN_FUNC("return with DF set", sec, insn->offset);
return 1;
}
if (func && has_modified_stack_frame(&state)) {
WARN_FUNC("return with modified stack frame",
sec, insn->offset);
@ -2172,6 +2183,20 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
state.uaccess = false;
break;
case INSN_STD:
if (state.df)
WARN_FUNC("recursive STD", sec, insn->offset);
state.df = true;
break;
case INSN_CLD:
if (!state.df && insn->func)
WARN_FUNC("redundant CLD", sec, insn->offset);
state.df = false;
break;
default:
break;
}

2
tools/objtool/check.h
View File

@ -31,7 +31,7 @@ struct insn_state {
int stack_size;
unsigned char type;
bool bp_scratch;
bool drap, end, uaccess;
bool drap, end, uaccess, df;
unsigned int uaccess_stack;
int drap_reg, drap_offset;
struct cfi_reg vals[CFI_NUM_REGS];