From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 30 Oct 2021 09:47:58 +0200
Subject: static_call,x86: Robustify trampoline patching
Git-commit: 2105a92748e83e2e3ee6be539da959706bbb3898
Patch-mainline: v5.16-rc1
References: bsc#1199657 CVE-2022-29900 CVE-2022-29901
Add a few signature bytes after the static call trampoline and verify
those bytes match before patching the trampoline. This avoids patching
random other JMPs (such as CFI jump-table entries) instead.
These bytes decode as:
d: 53 push %rbx
e: 43 54 rex.XB push %r12
And happen to spell "SCT".
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211030074758.GT174703@worktop.programming.kicks-ass.net
Acked-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/static_call.h | 1 +
arch/x86/kernel/static_call.c | 14 ++++++++++----
tools/objtool/check.c | 3 +++
3 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/static_call.h b/arch/x86/include/asm/static_call.h
index cbb67b6030f9..39ebe0511869 100644
--- a/arch/x86/include/asm/static_call.h
+++ b/arch/x86/include/asm/static_call.h
@@ -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")
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index ea028e736831..9c407a33a774 100644
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -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);
}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index add39902166d..21735829b860 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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