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x86/ibt, objtool: Add IBT_NOSEAL()

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Add a macro which prevents a function from getting sealed if there are
no compile-time references to it.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Message-Id: <20220818213927.e44fmxkoq4yj6ybn@treble>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Josh Poimboeuf 2022-08-18 14:39:27 -07:00 committed by Paolo Bonzini
parent 20ec3ebd70
commit e27e5bea95
2 changed files with 13 additions and 1 deletions
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11
arch/x86/include/asm/ibt.h
View File

@ -31,6 +31,16 @@
#define __noendbr __attribute__((nocf_check))
/*
* Create a dummy function pointer reference to prevent objtool from marking
* the function as needing to be "sealed" (i.e. ENDBR converted to NOP by
* apply_ibt_endbr()).
*/
#define IBT_NOSEAL(fname) \
".pushsection .discard.ibt_endbr_noseal\n\t" \
_ASM_PTR fname "\n\t" \
".popsection\n\t"
static inline __attribute_const__ u32 gen_endbr(void)
{
u32 endbr;
@ -84,6 +94,7 @@ extern __noendbr void ibt_restore(u64 save);
#ifndef __ASSEMBLY__
#define ASM_ENDBR
#define IBT_NOSEAL(name)
#define __noendbr

3
tools/objtool/check.c
View File

@ -4096,7 +4096,8 @@ static int validate_ibt(struct objtool_file *file)
* These sections can reference text addresses, but not with
* the intent to indirect branch to them.
*/
if (!strncmp(sec->name, ".discard", 8) ||
if ((!strncmp(sec->name, ".discard", 8) &&
strcmp(sec->name, ".discard.ibt_endbr_noseal")) ||
!strncmp(sec->name, ".debug", 6) ||
!strcmp(sec->name, ".altinstructions") ||
!strcmp(sec->name, ".ibt_endbr_seal") ||