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Message-ID: <173379676698.973433.16660904104531065153.stgit@devnote2>
Date: Tue, 10 Dec 2024 11:12:47 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Florent Revest <revest@...omium.org>
Cc: linux-trace-kernel@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
bpf <bpf@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Jiri Olsa <jolsa@...nel.org>,
Alan Maguire <alan.maguire@...cle.com>,
Mark Rutland <mark.rutland@....com>,
linux-arch@...r.kernel.org,
kernel test robot <lkp@...el.com>
Subject: [PATCH v21 19/20] ftrace: Add ftrace_get_symaddr to convert fentry_ip to symaddr
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
This introduces ftrace_get_symaddr() which tries to convert fentry_ip
passed by ftrace or fgraph callback to symaddr without calling
kallsyms API. It returns the symbol address or 0 if it fails to
convert it.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412061423.K79V55Hd-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202412061804.5VRzF14E-lkp@intel.com/
---
Changes in v21:
- On arm64, fix the macro name to ftrace_get_symaddr() correctly.
- Define ftrace_get_symaddr() outside of CONFIG_DYNAMIC_FTRACE.
Changes in v19:
- Newly added.
---
arch/arm64/include/asm/ftrace.h | 2 +
arch/arm64/kernel/ftrace.c | 63 +++++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/ftrace.h | 21 +++++++++++++
include/linux/ftrace.h | 13 ++++++++
4 files changed, 99 insertions(+)
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 876e88ad4119..bfe3ce9df197 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -52,6 +52,8 @@ extern unsigned long ftrace_graph_call;
extern void return_to_handler(void);
unsigned long ftrace_call_adjust(unsigned long addr);
+unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip);
+#define ftrace_get_symaddr(fentry_ip) arch_ftrace_get_symaddr(fentry_ip)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
#define HAVE_ARCH_FTRACE_REGS
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 570c38be833c..d7c0d023dfe5 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -143,6 +143,69 @@ unsigned long ftrace_call_adjust(unsigned long addr)
return addr;
}
+/* Convert fentry_ip to the symbol address without kallsyms */
+unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
+{
+ u32 insn;
+
+ /*
+ * When using patchable-function-entry without pre-function NOPS, ftrace
+ * entry is the address of the first NOP after the function entry point.
+ *
+ * The compiler has either generated:
+ *
+ * func+00: func: NOP // To be patched to MOV X9, LR
+ * func+04: NOP // To be patched to BL <caller>
+ *
+ * Or:
+ *
+ * func-04: BTI C
+ * func+00: func: NOP // To be patched to MOV X9, LR
+ * func+04: NOP // To be patched to BL <caller>
+ *
+ * The fentry_ip is the address of `BL <caller>` which is at `func + 4`
+ * bytes in either case.
+ */
+ if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
+ return fentry_ip - AARCH64_INSN_SIZE;
+
+ /*
+ * When using patchable-function-entry with pre-function NOPs, BTI is
+ * a bit different.
+ *
+ * func+00: func: NOP // To be patched to MOV X9, LR
+ * func+04: NOP // To be patched to BL <caller>
+ *
+ * Or:
+ *
+ * func+00: func: BTI C
+ * func+04: NOP // To be patched to MOV X9, LR
+ * func+08: NOP // To be patched to BL <caller>
+ *
+ * The fentry_ip is the address of `BL <caller>` which is at either
+ * `func + 4` or `func + 8` depends on whether there is a BTI.
+ */
+
+ /* If there is no BTI, the func address should be one instruction before. */
+ if (!IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))
+ return fentry_ip - AARCH64_INSN_SIZE;
+
+ /* We want to be extra safe in case entry ip is on the page edge,
+ * but otherwise we need to avoid get_kernel_nofault()'s overhead.
+ */
+ if ((fentry_ip & ~PAGE_MASK) < AARCH64_INSN_SIZE * 2) {
+ if (get_kernel_nofault(insn, (u32 *)(fentry_ip - AARCH64_INSN_SIZE * 2)))
+ return 0;
+ } else {
+ insn = *(u32 *)(fentry_ip - AARCH64_INSN_SIZE * 2);
+ }
+
+ if (aarch64_insn_is_bti(le32_to_cpu((__le32)insn)))
+ return fentry_ip - AARCH64_INSN_SIZE * 2;
+
+ return fentry_ip - AARCH64_INSN_SIZE;
+}
+
/*
* Replace a single instruction, which may be a branch or NOP.
* If @validate == true, a replaced instruction is checked against 'old'.
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index cc92c99ef276..f9cb4d07df58 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -34,6 +34,27 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
return addr;
}
+static inline unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
+{
+#ifdef CONFIG_X86_KERNEL_IBT
+ u32 instr;
+
+ /* We want to be extra safe in case entry ip is on the page edge,
+ * but otherwise we need to avoid get_kernel_nofault()'s overhead.
+ */
+ if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
+ if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
+ return fentry_ip;
+ } else {
+ instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
+ }
+ if (is_endbr(instr))
+ fentry_ip -= ENDBR_INSN_SIZE;
+#endif
+ return fentry_ip;
+}
+#define ftrace_get_symaddr(fentry_ip) arch_ftrace_get_symaddr(fentry_ip)
+
#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
#include <linux/ftrace_regs.h>
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 4c553fe9c026..07092dfb21a4 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -622,6 +622,19 @@ enum {
FTRACE_MAY_SLEEP = (1 << 5),
};
+/* Arches can override ftrace_get_symaddr() to convert fentry_ip to symaddr. */
+#ifndef ftrace_get_symaddr
+/**
+ * ftrace_get_symaddr - return the symbol address from fentry_ip
+ * @fentry_ip: the address of ftrace location
+ *
+ * Get the symbol address from @fentry_ip (fast path). If there is no fast
+ * search path, this returns 0.
+ * User may need to use kallsyms API to find the symbol address.
+ */
+#define ftrace_get_symaddr(fentry_ip) (0)
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
void ftrace_arch_code_modify_prepare(void);
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