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A single fix for static calls to make the trampoline patching more robust

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by placing explicit signature bytes after the call trampoline to prevent
 patching random other jumps like the CFI jump table entries.
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Merge tag 'locking-urgent-2021-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 static call update from Thomas Gleixner:
 "A single fix for static calls to make the trampoline patching more
  robust by placing explicit signature bytes after the call trampoline
  to prevent patching random other jumps like the CFI jump table
  entries"

* tag 'locking-urgent-2021-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  static_call,x86: Robustify trampoline patching
This commit is contained in:
Linus Torvalds 2021-11-14 10:30:17 -08:00
commit 218cc8b860
3 changed files with 14 additions and 4 deletions
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1
arch/x86/include/asm/static_call.h
View File

@ -27,6 +27,7 @@
".globl " STATIC_CALL_TRAMP_STR(name) " \n" \
STATIC_CALL_TRAMP_STR(name) ": \n" \
insns " \n" \
".byte 0x53, 0x43, 0x54 \n" \
".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \
".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
".popsection \n")

14
arch/x86/kernel/static_call.c
View File

@ -56,10 +56,15 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void
text_poke_bp(insn, code, size, emulate);
}
static void __static_call_validate(void *insn, bool tail)
static void __static_call_validate(void *insn, bool tail, bool tramp)
{
u8 opcode = *(u8 *)insn;
if (tramp && memcmp(insn+5, "SCT", 3)) {
pr_err("trampoline signature fail");
BUG();
}
if (tail) {
if (opcode == JMP32_INSN_OPCODE ||
opcode == RET_INSN_OPCODE)
@ -74,7 +79,8 @@ static void __static_call_validate(void *insn, bool tail)
/*
* If we ever trigger this, our text is corrupt, we'll probably not live long.
*/
WARN_ONCE(1, "unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
BUG();
}
static inline enum insn_type __sc_insn(bool null, bool tail)
@ -97,12 +103,12 @@ void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
mutex_lock(&text_mutex);
if (tramp) {
__static_call_validate(tramp, true);
__static_call_validate(tramp, true, true);
__static_call_transform(tramp, __sc_insn(!func, true), func);
}
if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
__static_call_validate(site, tail);
__static_call_validate(site, tail, false);
__static_call_transform(site, __sc_insn(!func, tail), func);
}

3
tools/objtool/check.c
View File

@ -3310,6 +3310,9 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
if (!insn->func)
return false;
if (insn->func->static_call_tramp)
return true;
/*
* CONFIG_UBSAN_TRAP inserts a UD2 when it sees
* __builtin_unreachable(). The BUG() macro has an unreachable() after