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objtool: Fix noinstr vs KCOV 

Since many compilers cannot disable KCOV with a function attribute,
help it to NOP out any __sanitizer_cov_*() calls injected in noinstr
code.

This turns:

12:   e8 00 00 00 00          callq  17 <lockdep_hardirqs_on+0x17>
		13: R_X86_64_PLT32      __sanitizer_cov_trace_pc-0x4

into:

12:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
		13: R_X86_64_NONE      __sanitizer_cov_trace_pc-0x4

Just like recordmcount does.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
This commit is contained in:
Peter Zijlstra 2020-06-12 16:05:26 +02:00
parent fdabdd0b05
commit 0f1441b44e
5 changed files with 46 additions and 1 deletions
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2
arch/x86/Kconfig
View File

@ -67,7 +67,7 @@ config X86
select ARCH_HAS_FILTER_PGPROT
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_KCOV if X86_64
select ARCH_HAS_KCOV if X86_64 && STACK_VALIDATION
select ARCH_HAS_MEM_ENCRYPT
select ARCH_HAS_MEMBARRIER_SYNC_CORE
select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE

2
tools/objtool/arch.h
View File

@ -84,4 +84,6 @@ unsigned long arch_jump_destination(struct instruction *insn);
unsigned long arch_dest_rela_offset(int addend);
const char *arch_nop_insn(int len);
#endif /* _ARCH_H */

18
tools/objtool/arch/x86/decode.c
View File

@ -565,3 +565,21 @@ void arch_initial_func_cfi_state(struct cfi_init_state *state)
state->regs[16].base = CFI_CFA;
state->regs[16].offset = -8;
}
const char *arch_nop_insn(int len)
{
static const char nops[5][5] = {
/* 1 */ { 0x90 },
/* 2 */ { 0x66, 0x90 },
/* 3 */ { 0x0f, 0x1f, 0x00 },
/* 4 */ { 0x0f, 0x1f, 0x40, 0x00 },
/* 5 */ { 0x0f, 0x1f, 0x44, 0x00, 0x00 },
};
if (len < 1 || len > 5) {
WARN("invalid NOP size: %d\n", len);
return NULL;
}
return nops[len-1];
}

6
tools/objtool/arch/x86/include/arch_elf.h Normal file
View File

@ -0,0 +1,6 @@
#ifndef _OBJTOOL_ARCH_ELF
#define _OBJTOOL_ARCH_ELF
#define R_NONE R_X86_64_NONE
#endif /* _OBJTOOL_ARCH_ELF */

19
tools/objtool/check.c
View File

@ -12,6 +12,7 @@
#include "check.h"
#include "special.h"
#include "warn.h"
#include "arch_elf.h"
#include <linux/hashtable.h>
#include <linux/kernel.h>
@ -765,6 +766,24 @@ static int add_call_destinations(struct objtool_file *file)
} else
insn->call_dest = rela->sym;
/*
* Many compilers cannot disable KCOV with a function attribute
* so they need a little help, NOP out any KCOV calls from noinstr
* text.
*/
if (insn->sec->noinstr &&
!strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
if (rela) {
rela->type = R_NONE;
elf_write_rela(file->elf, rela);
}
elf_write_insn(file->elf, insn->sec,
insn->offset, insn->len,
arch_nop_insn(insn->len));
insn->type = INSN_NOP;
}
/*
* Whatever stack impact regular CALLs have, should be undone
* by the RETURN of the called function.