This is a note to let you know that I've just added the patch titled
x86/returnthunk: Allow different return thunks
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-returnthunk-allow-different-return-thunks.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 f169c7403c60b56e66c136af415076558a563d6e Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu, 15 Sep 2022 13:11:25 +0200
Subject: x86/returnthunk: Allow different return thunks
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Upstream commit: 770ae1b709528a6a173b5c7b183818ee9b45e376
In preparation for call depth tracking on Intel SKL CPUs, make it possible
to patch in a SKL specific return thunk.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220915111147.680469665@xxxxxxxxxxxxx
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/nospec-branch.h | 6 ++++++
arch/x86/kernel/alternative.c | 19 ++++++++++++++-----
arch/x86/kernel/ftrace.c | 2 +-
arch/x86/kernel/static_call.c | 2 +-
arch/x86/net/bpf_jit_comp.c | 2 +-
5 files changed, 23 insertions(+), 8 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -222,6 +222,12 @@ extern void srso_alias_untrain_ret(void)
extern void entry_untrain_ret(void);
extern void entry_ibpb(void);
+#ifdef CONFIG_CALL_THUNKS
+extern void (*x86_return_thunk)(void);
+#else
+#define x86_return_thunk (&__x86_return_thunk)
+#endif
+
#ifdef CONFIG_RETPOLINE
#define GEN(reg) \
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -536,6 +536,11 @@ void __init_or_module noinline apply_ret
}
#ifdef CONFIG_RETHUNK
+
+#ifdef CONFIG_CALL_THUNKS
+void (*x86_return_thunk)(void) __ro_after_init = &__x86_return_thunk;
+#endif
+
/*
* Rewrite the compiler generated return thunk tail-calls.
*
@@ -551,14 +556,18 @@ static int patch_return(void *addr, stru
{
int i = 0;
- if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
- return -1;
-
- bytes[i++] = RET_INSN_OPCODE;
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) {
+ if (x86_return_thunk == __x86_return_thunk)
+ return -1;
+
+ i = JMP32_INSN_SIZE;
+ __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i);
+ } else {
+ bytes[i++] = RET_INSN_OPCODE;
+ }
for (; i < insn->length;)
bytes[i++] = INT3_INSN_OPCODE;
-
return i;
}
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -361,7 +361,7 @@ create_trampoline(struct ftrace_ops *ops
ip = trampoline + size;
if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
- __text_gen_insn(ip, JMP32_INSN_OPCODE, ip, &__x86_return_thunk, JMP32_INSN_SIZE);
+ __text_gen_insn(ip, JMP32_INSN_OPCODE, ip, x86_return_thunk, JMP32_INSN_SIZE);
else
memcpy(ip, retq, sizeof(retq));
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -80,7 +80,7 @@ static void __ref __static_call_transfor
case RET:
if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
- code = text_gen_insn(JMP32_INSN_OPCODE, insn, &__x86_return_thunk);
+ code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk);
else
code = &retinsn;
break;
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -432,7 +432,7 @@ static void emit_return(u8 **pprog, u8 *
u8 *prog = *pprog;
if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) {
- emit_jump(&prog, &__x86_return_thunk, ip);
+ emit_jump(&prog, x86_return_thunk, ip);
} else {
EMIT1(0xC3); /* ret */
if (IS_ENABLED(CONFIG_SLS))
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-6.1/x86-alternative-make-custom-return-thunk-unconditional.patch
queue-6.1/x86-returnthunk-allow-different-return-thunks.patch
queue-6.1/sched-rt-sysctl_sched_rr_timeslice-show-default-timeslice-after-reset.patch
