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Peter Zijlstra says: 

Address KCOV vs noinstr. There is no function attribute to selectively
 suppress KCOV instrumentation, instead teach objtool to NOP out the
 calls in noinstr functions.
 
 This cures a bunch of KCOV crashes (as used by syzcaller).
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Merge tag 'objtool_urgent_for_5.8_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool fixes from Borislav Petkov:
 "Three fixes from Peter Zijlstra suppressing KCOV instrumentation in
  noinstr sections.

  Peter Zijlstra says:
    "Address KCOV vs noinstr. There is no function attribute to
     selectively suppress KCOV instrumentation, instead teach objtool
     to NOP out the calls in noinstr functions"

  This cures a bunch of KCOV crashes (as used by syzcaller)"

* tag 'objtool_urgent_for_5.8_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Fix noinstr vs KCOV
  objtool: Provide elf_write_{insn,reloc}()
  objtool: Clean up elf_write() condition
This commit is contained in:
Linus Torvalds 2020-06-28 10:16:15 -07:00
parent a358505d8a 0f1441b44e
commit 7ecb59a566
8 changed files with 109 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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 */

23
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.
@ -2766,7 +2785,7 @@ int check(const char *_objname, bool orc)
objname = _objname;
file.elf = elf_open_read(objname, orc ? O_RDWR : O_RDONLY);
file.elf = elf_open_read(objname, O_RDWR);
if (!file.elf)
return 1;
@ -2827,7 +2846,9 @@ int check(const char *_objname, bool orc)
ret = create_orc_sections(&file);
if (ret < 0)
goto out;
}
if (file.elf->changed) {
ret = elf_write(file.elf);
if (ret < 0)
goto out;

53
tools/objtool/elf.c
View File

@ -529,8 +529,9 @@ static int read_relas(struct elf *elf)
rela->addend = rela->rela.r_addend;
rela->offset = rela->rela.r_offset;
symndx = GELF_R_SYM(rela->rela.r_info);
rela->sym = find_symbol_by_index(elf, symndx);
rela->sec = sec;
rela->idx = i;
rela->sym = find_symbol_by_index(elf, symndx);
if (!rela->sym) {
WARN("can't find rela entry symbol %d for %s",
symndx, sec->name);
@ -713,6 +714,8 @@ struct section *elf_create_section(struct elf *elf, const char *name,
elf_hash_add(elf->section_hash, &sec->hash, sec->idx);
elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name));
elf->changed = true;
return sec;
}
@ -746,7 +749,7 @@ struct section *elf_create_rela_section(struct elf *elf, struct section *base)
return sec;
}
int elf_rebuild_rela_section(struct section *sec)
int elf_rebuild_rela_section(struct elf *elf, struct section *sec)
{
struct rela *rela;
int nr, idx = 0, size;
@ -763,6 +766,9 @@ int elf_rebuild_rela_section(struct section *sec)
return -1;
}
sec->changed = true;
elf->changed = true;
sec->data->d_buf = relas;
sec->data->d_size = size;
@ -779,7 +785,44 @@ int elf_rebuild_rela_section(struct section *sec)
return 0;
}
int elf_write(const struct elf *elf)
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn)
{
Elf_Data *data = sec->data;
if (data->d_type != ELF_T_BYTE || data->d_off) {
WARN("write to unexpected data for section: %s", sec->name);
return -1;
}
memcpy(data->d_buf + offset, insn, len);
elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
elf->changed = true;
return 0;
}
int elf_write_rela(struct elf *elf, struct rela *rela)
{
struct section *sec = rela->sec;
rela->rela.r_info = GELF_R_INFO(rela->sym->idx, rela->type);
rela->rela.r_addend = rela->addend;
rela->rela.r_offset = rela->offset;
if (!gelf_update_rela(sec->data, rela->idx, &rela->rela)) {
WARN_ELF("gelf_update_rela");
return -1;
}
elf->changed = true;
return 0;
}
int elf_write(struct elf *elf)
{
struct section *sec;
Elf_Scn *s;
@ -796,6 +839,8 @@ int elf_write(const struct elf *elf)
WARN_ELF("gelf_update_shdr");
return -1;
}
sec->changed = false;
}
}
@ -808,6 +853,8 @@ int elf_write(const struct elf *elf)
return -1;
}
elf->changed = false;
return 0;
}

12
tools/objtool/elf.h
View File

@ -64,9 +64,10 @@ struct rela {
GElf_Rela rela;
struct section *sec;
struct symbol *sym;
unsigned int type;
unsigned long offset;
unsigned int type;
int addend;
int idx;
bool jump_table_start;
};
@ -76,6 +77,7 @@ struct elf {
Elf *elf;
GElf_Ehdr ehdr;
int fd;
bool changed;
char *name;
struct list_head sections;
DECLARE_HASHTABLE(symbol_hash, ELF_HASH_BITS);
@ -118,7 +120,11 @@ struct elf *elf_open_read(const char *name, int flags);
struct section *elf_create_section(struct elf *elf, const char *name, size_t entsize, int nr);
struct section *elf_create_rela_section(struct elf *elf, struct section *base);
void elf_add_rela(struct elf *elf, struct rela *rela);
int elf_write(const struct elf *elf);
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn);
int elf_write_rela(struct elf *elf, struct rela *rela);
int elf_write(struct elf *elf);
void elf_close(struct elf *elf);
struct section *find_section_by_name(const struct elf *elf, const char *name);
@ -130,7 +136,7 @@ struct rela *find_rela_by_dest(const struct elf *elf, struct section *sec, unsig
struct rela *find_rela_by_dest_range(const struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len);
struct symbol *find_func_containing(struct section *sec, unsigned long offset);
int elf_rebuild_rela_section(struct section *sec);
int elf_rebuild_rela_section(struct elf *elf, struct section *sec);
#define for_each_sec(file, sec) \
list_for_each_entry(sec, &file->elf->sections, list)

2
tools/objtool/orc_gen.c
View File

@ -222,7 +222,7 @@ int create_orc_sections(struct objtool_file *file)
}
}
if (elf_rebuild_rela_section(ip_relasec))
if (elf_rebuild_rela_section(file->elf, ip_relasec))
return -1;
return 0;