mirrors
/
linux-stable
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
1
0
Fork 0
Code Issues Releases Wiki Activity

objtool: Rework ibt and extricate from stack validation 

Extricate ibt from validate_branch() so they can be executed (or ported)
independently from each other.

While shuffling code around, simplify and improve the ibt logic:

- Ignore an explicit list of known sections which reference functions
  for reasons other than indirect branching to them.  This helps prevent
  unnnecesary sealing.

- Warn on missing !ENDBR for all other sections, not just .data and
  .rodata.  This finds additional warnings, because there are sections
  other than .[ro]data which reference function pointers.  For example,
  the ksymtab sections which are used for exporting symbols.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/fd1435e46bb95f81031b8fb1fa360f5f787e4316.1650300597.git.jpoimboe@redhat.com
This commit is contained in:
Josh Poimboeuf 2022-04-18 09:50:34 -07:00 committed by Peter Zijlstra
parent 7dce62041a
commit 3c6f9f77e6
1 changed files with 151 additions and 137 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

288
tools/objtool/check.c
View File

@ -3182,114 +3182,6 @@ static struct instruction *next_insn_to_validate(struct objtool_file *file,
return next_insn_same_sec(file, insn);
}
static struct instruction *
validate_ibt_reloc(struct objtool_file *file, struct reloc *reloc)
{
struct instruction *dest;
struct section *sec;
unsigned long off;
sec = reloc->sym->sec;
off = reloc->sym->offset;
if ((reloc->sec->base->sh.sh_flags & SHF_EXECINSTR) &&
(reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32))
off += arch_dest_reloc_offset(reloc->addend);
else
off += reloc->addend;
dest = find_insn(file, sec, off);
if (!dest)
return NULL;
if (dest->type == INSN_ENDBR) {
if (!list_empty(&dest->call_node))
list_del_init(&dest->call_node);
return NULL;
}
if (reloc->sym->static_call_tramp)
return NULL;
return dest;
}
static void warn_noendbr(const char *msg, struct section *sec, unsigned long offset,
struct instruction *dest)
{
WARN_FUNC("%srelocation to !ENDBR: %s", sec, offset, msg,
offstr(dest->sec, dest->offset));
}
static void validate_ibt_dest(struct objtool_file *file, struct instruction *insn,
struct instruction *dest)
{
if (dest->func && dest->func == insn->func) {
/*
* Anything from->to self is either _THIS_IP_ or IRET-to-self.
*
* There is no sane way to annotate _THIS_IP_ since the compiler treats the
* relocation as a constant and is happy to fold in offsets, skewing any
* annotation we do, leading to vast amounts of false-positives.
*
* There's also compiler generated _THIS_IP_ through KCOV and
* such which we have no hope of annotating.
*
* As such, blanket accept self-references without issue.
*/
return;
}
if (dest->noendbr)
return;
warn_noendbr("", insn->sec, insn->offset, dest);
}
static void validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
{
struct instruction *dest;
struct reloc *reloc;
switch (insn->type) {
case INSN_CALL:
case INSN_CALL_DYNAMIC:
case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
case INSN_JUMP_DYNAMIC:
case INSN_JUMP_DYNAMIC_CONDITIONAL:
case INSN_RETURN:
/*
* We're looking for code references setting up indirect code
* flow. As such, ignore direct code flow and the actual
* dynamic branches.
*/
return;
case INSN_NOP:
/*
* handle_group_alt() will create INSN_NOP instruction that
* don't belong to any section, ignore all NOP since they won't
* carry a (useful) relocation anyway.
*/
return;
default:
break;
}
for (reloc = insn_reloc(file, insn);
reloc;
reloc = find_reloc_by_dest_range(file->elf, insn->sec,
reloc->offset + 1,
(insn->offset + insn->len) - (reloc->offset + 1))) {
dest = validate_ibt_reloc(file, reloc);
if (dest)
validate_ibt_dest(file, insn, dest);
}
}
/*
* Follow the branch starting at the given instruction, and recursively follow
* any other branches (jumps). Meanwhile, track the frame pointer state at
@ -3499,9 +3391,6 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
break;
}
if (opts.ibt)
validate_ibt_insn(file, insn);
if (insn->dead_end)
return 0;
@ -3787,48 +3676,173 @@ static int validate_functions(struct objtool_file *file)
return warnings;
}
static void mark_endbr_used(struct instruction *insn)
{
if (!list_empty(&insn->call_node))
list_del_init(&insn->call_node);
}
static int validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
{
struct instruction *dest;
struct reloc *reloc;
unsigned long off;
int warnings = 0;
/*
* Looking for function pointer load relocations. Ignore
* direct/indirect branches:
*/
switch (insn->type) {
case INSN_CALL:
case INSN_CALL_DYNAMIC:
case INSN_JUMP_CONDITIONAL:
case INSN_JUMP_UNCONDITIONAL:
case INSN_JUMP_DYNAMIC:
case INSN_JUMP_DYNAMIC_CONDITIONAL:
case INSN_RETURN:
case INSN_NOP:
return 0;
default:
break;
}
for (reloc = insn_reloc(file, insn);
reloc;
reloc = find_reloc_by_dest_range(file->elf, insn->sec,
reloc->offset + 1,
(insn->offset + insn->len) - (reloc->offset + 1))) {
/*
* static_call_update() references the trampoline, which
* doesn't have (or need) ENDBR. Skip warning in that case.
*/
if (reloc->sym->static_call_tramp)
continue;
off = reloc->sym->offset;
if (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32)
off += arch_dest_reloc_offset(reloc->addend);
else
off += reloc->addend;
dest = find_insn(file, reloc->sym->sec, off);
if (!dest)
continue;
if (dest->type == INSN_ENDBR) {
mark_endbr_used(dest);
continue;
}
if (dest->func && dest->func == insn->func) {
/*
* Anything from->to self is either _THIS_IP_ or
* IRET-to-self.
*
* There is no sane way to annotate _THIS_IP_ since the
* compiler treats the relocation as a constant and is
* happy to fold in offsets, skewing any annotation we
* do, leading to vast amounts of false-positives.
*
* There's also compiler generated _THIS_IP_ through
* KCOV and such which we have no hope of annotating.
*
* As such, blanket accept self-references without
* issue.
*/
continue;
}
if (dest->noendbr)
continue;
WARN_FUNC("relocation to !ENDBR: %s",
insn->sec, insn->offset,
offstr(dest->sec, dest->offset));
warnings++;
}
return warnings;
}
static int validate_ibt_data_reloc(struct objtool_file *file,
struct reloc *reloc)
{
struct instruction *dest;
dest = find_insn(file, reloc->sym->sec,
reloc->sym->offset + reloc->addend);
if (!dest)
return 0;
if (dest->type == INSN_ENDBR) {
mark_endbr_used(dest);
return 0;
}
if (dest->noendbr)
return 0;
WARN_FUNC("data relocation to !ENDBR: %s",
reloc->sec->base, reloc->offset,
offstr(dest->sec, dest->offset));
return 1;
}
/*
* Validate IBT rules and remove used ENDBR instructions from the seal list.
* Unused ENDBR instructions will be annotated for sealing (i.e., replaced with
* NOPs) later, in create_ibt_endbr_seal_sections().
*/
static int validate_ibt(struct objtool_file *file)
{
struct section *sec;
struct reloc *reloc;
struct instruction *insn;
int warnings = 0;
for_each_insn(file, insn)
warnings += validate_ibt_insn(file, insn);
for_each_sec(file, sec) {
bool is_data;
/* already done in validate_branch() */
/* Already done by validate_ibt_insn() */
if (sec->sh.sh_flags & SHF_EXECINSTR)
continue;
if (!sec->reloc)
continue;
if (!strncmp(sec->name, ".orc", 4))
/*
* These sections can reference text addresses, but not with
* the intent to indirect branch to them.
*/
if (!strncmp(sec->name, ".discard", 8) ||
!strncmp(sec->name, ".debug", 6) ||
!strcmp(sec->name, ".altinstructions") ||
!strcmp(sec->name, ".ibt_endbr_seal") ||
!strcmp(sec->name, ".orc_unwind_ip") ||
!strcmp(sec->name, ".parainstructions") ||
!strcmp(sec->name, ".retpoline_sites") ||
!strcmp(sec->name, ".smp_locks") ||
!strcmp(sec->name, ".static_call_sites") ||
!strcmp(sec->name, "_error_injection_whitelist") ||
!strcmp(sec->name, "_kprobe_blacklist") ||
!strcmp(sec->name, "__bug_table") ||
!strcmp(sec->name, "__ex_table") ||
!strcmp(sec->name, "__jump_table") ||
!strcmp(sec->name, "__mcount_loc") ||
!strcmp(sec->name, "__tracepoints"))
continue;
if (!strncmp(sec->name, ".discard", 8))
continue;
if (!strncmp(sec->name, ".debug", 6))
continue;
if (!strcmp(sec->name, "_error_injection_whitelist"))
continue;
if (!strcmp(sec->name, "_kprobe_blacklist"))
continue;
is_data = strstr(sec->name, ".data") || strstr(sec->name, ".rodata");
list_for_each_entry(reloc, &sec->reloc->reloc_list, list) {
struct instruction *dest;
dest = validate_ibt_reloc(file, reloc);
if (is_data && dest && !dest->noendbr)
warn_noendbr("data ", sec, reloc->offset, dest);
}
list_for_each_entry(reloc, &sec->reloc->reloc_list, list)
warnings += validate_ibt_data_reloc(file, reloc);
}
return 0;
return warnings;
}
static int validate_reachable_instructions(struct objtool_file *file)
@ -3899,7 +3913,7 @@ int check(struct objtool_file *file)
warnings += ret;
}
if (opts.stackval || opts.orc || opts.uaccess || opts.ibt || opts.sls) {
if (opts.stackval || opts.orc || opts.uaccess || opts.sls) {
ret = validate_functions(file);
if (ret < 0)
goto out;