This is a note to let you know that I've just added the patch titled
x86/static_call: Add support for Jcc tail-calls
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-static_call-add-support-for-jcc-tail-calls.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From db720e3226a717120221095b2ddbbac34da79ec0 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu, 26 Jan 2023 16:34:27 +0100
Subject: x86/static_call: Add support for Jcc tail-calls
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 923510c88d2b7d947c4217835fd9ca6bd65cc56c upstream.
Clang likes to create conditional tail calls like:
0000000000000350 <amd_pmu_add_event>:
350: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 351: R_X86_64_NONE __fentry__-0x4
355: 48 83 bf 20 01 00 00 00 cmpq $0x0,0x120(%rdi)
35d: 0f 85 00 00 00 00 jne 363 <amd_pmu_add_event+0x13> 35f: R_X86_64_PLT32 __SCT__amd_pmu_branch_add-0x4
363: e9 00 00 00 00 jmp 368 <amd_pmu_add_event+0x18> 364: R_X86_64_PLT32 __x86_return_thunk-0x4
Where 0x35d is a static call site that's turned into a conditional
tail-call using the Jcc class of instructions.
Teach the in-line static call text patching about this.
Notably, since there is no conditional-ret, in that case patch the Jcc
to point at an empty stub function that does the ret -- or the return
thunk when needed.
Reported-by: "Erhard F." <erhard_f@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Link: https://lore.kernel.org/r/Y9Kdg9QjHkr9G5b5@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[nathan: Backport to 6.1:
- Use __x86_return_thunk instead of x86_return_thunk for func in
__static_call_transform()
- Remove ASM_FUNC_ALIGN in __static_call_return() asm, as call
depth tracking was merged in 6.2]
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/static_call.c | 49 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 46 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -9,6 +9,7 @@ enum insn_type {
NOP = 1, /* site cond-call */
JMP = 2, /* tramp / site tail-call */
RET = 3, /* tramp / site cond-tail-call */
+ JCC = 4,
};
/*
@@ -25,12 +26,39 @@ static const u8 xor5rax[] = { 0x2e, 0x2e
static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
+static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */
+{
+ u8 ret = 0;
+
+ if (insn[0] == 0x0f) {
+ u8 tmp = insn[1];
+ if ((tmp & 0xf0) == 0x80)
+ ret = tmp;
+ }
+
+ return ret;
+}
+
+extern void __static_call_return(void);
+
+asm (".global __static_call_return\n\t"
+ ".type __static_call_return, @function\n\t"
+ "__static_call_return:\n\t"
+ ANNOTATE_NOENDBR
+ ANNOTATE_RETPOLINE_SAFE
+ "ret; int3\n\t"
+ ".size __static_call_return, . - __static_call_return \n\t");
+
static void __ref __static_call_transform(void *insn, enum insn_type type,
void *func, bool modinit)
{
const void *emulate = NULL;
int size = CALL_INSN_SIZE;
const void *code;
+ u8 op, buf[6];
+
+ if ((type == JMP || type == RET) && (op = __is_Jcc(insn)))
+ type = JCC;
switch (type) {
case CALL:
@@ -56,6 +84,20 @@ static void __ref __static_call_transfor
else
code = &retinsn;
break;
+
+ case JCC:
+ if (!func) {
+ func = __static_call_return;
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+ func = __x86_return_thunk;
+ }
+
+ buf[0] = 0x0f;
+ __text_gen_insn(buf+1, op, insn+1, func, 5);
+ code = buf;
+ size = 6;
+
+ break;
}
if (memcmp(insn, code, size) == 0)
@@ -67,9 +109,9 @@ static void __ref __static_call_transfor
text_poke_bp(insn, code, size, emulate);
}
-static void __static_call_validate(void *insn, bool tail, bool tramp)
+static void __static_call_validate(u8 *insn, bool tail, bool tramp)
{
- u8 opcode = *(u8 *)insn;
+ u8 opcode = insn[0];
if (tramp && memcmp(insn+5, tramp_ud, 3)) {
pr_err("trampoline signature fail");
@@ -78,7 +120,8 @@ static void __static_call_validate(void
if (tail) {
if (opcode == JMP32_INSN_OPCODE ||
- opcode == RET_INSN_OPCODE)
+ opcode == RET_INSN_OPCODE ||
+ __is_Jcc(insn))
return;
} else {
if (opcode == CALL_INSN_OPCODE ||
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-6.1/sched-psi-stop-relying-on-timer_pending-for-poll_wor.patch
queue-6.1/x86-static_call-add-support-for-jcc-tail-calls.patch
queue-6.1/x86-alternatives-introduce-int3_emulate_jcc.patch
queue-6.1/x86-alternatives-teach-text_poke_bp-to-patch-jcc.d32-instructions.patch
