[tip: x86/core] x86/returnthunk: Allow different return thunks

tip-bot2 for Peter Zijlstra
2022-10-17T14:54:38Z

The following commit has been merged into the x86/core branch of tip:

Commit-ID: 770ae1b709528a6a173b5c7b183818ee9b45e376
Gitweb: https://git.kernel.org/tip/770ae1b709528a6a173b5c7b183818ee9b45e376
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 15 Sep 2022 13:11:25 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 17 Oct 2022 16:41:14 +02:00

x86/returnthunk: Allow different return thunks

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@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111147.680469665@infradead.org
---
arch/x86/include/asm/nospec-branch.h | 6 ++++++
arch/x86/kernel/alternative.c | 17 +++++++++++++----
arch/x86/kernel/ftrace.c | 2 +-
arch/x86/kernel/static_call.c | 2 +-
arch/x86/net/bpf_jit_comp.c | 2 +-
5 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index c936ce9..f10ca33 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -208,6 +208,12 @@ extern void __x86_return_thunk(void);
extern void zen_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) \
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 963872d..04d1e3d 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -518,6 +518,11 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
}

#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.
*
@@ -533,14 +538,18 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes)
{
int i = 0;

- if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
- return -1;
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) {
+ if (x86_return_thunk == __x86_return_thunk)
+ return -1;

- bytes[i++] = RET_INSN_OPCODE;
+ 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;
}

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 00eac45..4ac6692 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -359,7 +359,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)

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));

diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index aaaba85..5d3844a 100644
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -52,7 +52,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type,

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;
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9962042..0df391e 100644
--- 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 *ip)
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))