[PATCH v18 17/17] bpf: Add get_entry_ip() for arm64

Masami Hiramatsu (Google)
2024-10-26T04:39:02Z

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add get_entry_ip() implementation for arm64. This is based on the
information in ftrace_call_adjust() on arm64. Basically function entry
address = ftrace call entry_ip - 4, but when there is a BTI at the first
instruction, we need one more instruction back (entry_ip - 8.)

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
kernel/trace/bpf_trace.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 64 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 1532e9172bf9..d58d1417cbaa 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1042,6 +1042,70 @@ static unsigned long get_entry_ip(unsigned long fentry_ip)
fentry_ip -= ENDBR_INSN_SIZE;
return fentry_ip;
}
+#elif defined(CONFIG_ARM64)
+#include <asm/insn.h>
+
+static unsigned long get_entry_ip(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 fentry_ip - AARCH64_INSN_SIZE;
+ } 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;
+}
#else
#define get_entry_ip(fentry_ip) fentry_ip
#endif