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Message-ID: <20251027181749.240466-1-benniu@meta.com>
Date: Mon, 27 Oct 2025 11:17:49 -0700
From: Ben Niu <benniu@...a.com>
To: Catalin Marinas <catalin.marinas@....com>
CC: Will Deacon <will@...nel.org>, <tytso@....edu>, <Jason@...c4.com>,
Ben Niu
<benniu@...a.com>, Ben Niu <niuben003@...il.com>,
<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] tracing: Enable kprobe tracing for Arm64 asm functions
Currently, Arm64 assembly functions always have a bti c
instruction inserted before the prologue. When ftrace is enabled,
no padding nops are inserted at all.
This breaks kprobe tracing for asm functions, which assumes that
proper nops are added before and within functions (when ftrace is
enabled) and bti c is only present when CONFIG_ARM64_BTI_KERNEL is
defined.
The patch fixes the bug by inserting nops and bti c in Arm64 asm
in the same way as compiled C code.
Note: although this patch unblocks kprobe tracing, fentry is still
broken because no BTF info gets generated from assembly files. A
separate patch is needed to fix that.
I built this patch with different combos of the following features
and confirmed kprobe tracing for asm function __arch_copy_to_user
worked in all cases:
CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
CONFIG_DYNAMIC_FTRACE_WITH_ARGS
CONFIG_ARM64_BTI_KERNEL
Signed-off-by: Ben Niu <benniu@...a.com>
---
arch/arm64/include/asm/linkage.h | 103 ++++++++++++++++-----
arch/arm64/kernel/vdso/vgetrandom-chacha.S | 2 +-
2 files changed, 81 insertions(+), 24 deletions(-)
diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index d3acd9c87509..f3f3bc168162 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -5,8 +5,47 @@
#include <asm/assembler.h>
#endif
-#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT
-#define __ALIGN_STR ".balign " #CONFIG_FUNCTION_ALIGNMENT
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT
+#define __ALIGN_STR ".balign " #CONFIG_FUNCTION_ALIGNMENT
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
+
+#define PRE_FUNCTION_NOPS \
+ ALIGN; \
+ nops CONFIG_FUNCTION_ALIGNMENT / 4 - 2; \
+ .pushsection __patchable_function_entries, "awo", @progbits, .text; \
+ .p2align 3; \
+ .8byte 1f; \
+ .popsection; \
+ 1 :; \
+ nops 2;
+
+#define PRE_PROLOGUE_NOPS nops 2;
+
+#elif defined(CONFIG_DYNAMIC_FTRACE_WITH_ARGS)
+
+#define PRE_FUNCTION_NOPS
+
+#define PRE_PROLOGUE_NOPS \
+ .pushsection __patchable_function_entries, "awo", @progbits, .text; \
+ .p2align 3; \
+ .8byte 1f; \
+ .popsection; \
+ 1 :; \
+ nops 2;
+
+#else
+
+#define PRE_FUNCTION_NOPS
+#define PRE_PROLOGUE_NOPS
+
+#endif
+
+#ifdef CONFIG_ARM64_BTI_KERNEL
+#define BTI_C bti c;
+#else
+#define BTI_C
+#endif
/*
* When using in-kernel BTI we need to ensure that PCS-conformant
@@ -15,32 +54,50 @@
* everything, the override is done unconditionally so we're more
* likely to notice any drift from the overridden definitions.
*/
-#define SYM_FUNC_START(name) \
- SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
- bti c ;
+#define SYM_FUNC_START(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
+
+#define SYM_FUNC_START_NOTRACE(name) \
+ SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
+ BTI_C
-#define SYM_FUNC_START_NOALIGN(name) \
- SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE) \
- bti c ;
+#define SYM_FUNC_START_NOALIGN(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
-#define SYM_FUNC_START_LOCAL(name) \
- SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN) \
- bti c ;
+#define SYM_FUNC_START_LOCAL(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
-#define SYM_FUNC_START_LOCAL_NOALIGN(name) \
- SYM_START(name, SYM_L_LOCAL, SYM_A_NONE) \
- bti c ;
+#define SYM_FUNC_START_LOCAL_NOALIGN(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_LOCAL, SYM_A_NONE) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
-#define SYM_FUNC_START_WEAK(name) \
- SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN) \
- bti c ;
+#define SYM_FUNC_START_WEAK(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
-#define SYM_FUNC_START_WEAK_NOALIGN(name) \
- SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \
- bti c ;
+#define SYM_FUNC_START_WEAK_NOALIGN(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
-#define SYM_TYPED_FUNC_START(name) \
- SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
- bti c ;
+#define SYM_TYPED_FUNC_START(name) \
+ PRE_FUNCTION_NOPS \
+ SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \
+ BTI_C \
+ PRE_PROLOGUE_NOPS
#endif
diff --git a/arch/arm64/kernel/vdso/vgetrandom-chacha.S b/arch/arm64/kernel/vdso/vgetrandom-chacha.S
index 67890b445309..21c27b64cf9f 100644
--- a/arch/arm64/kernel/vdso/vgetrandom-chacha.S
+++ b/arch/arm64/kernel/vdso/vgetrandom-chacha.S
@@ -40,7 +40,7 @@
* x2: 8-byte counter input/output
* x3: number of 64-byte block to write to output
*/
-SYM_FUNC_START(__arch_chacha20_blocks_nostack)
+SYM_FUNC_START_NOTRACE(__arch_chacha20_blocks_nostack)
/* copy0 = "expand 32-byte k" */
mov_q x8, 0x3320646e61707865
--
2.47.3
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