Re: [PATCH v7 5/7] arm64: Add trampoline code for kretprobes
From: David Long
Date: Wed Jun 17 2015 - 14:37:12 EST
On 06/16/15 11:09, William Cohen wrote:
On 06/15/2015 03:07 PM, David Long wrote:
From: William Cohen <wcohen@xxxxxxxxxx>
The trampoline code is used by kretprobes to capture a return from a probed
function. This is done by saving the registers, calling the handler, and
restoring the registers. The code then returns to the roginal saved caller
s/roginal/original
Hopefully no one wants a v8 if it turns out only to be to fix this typo
in the commit description. I'll keep this in mind if a respin is needed
for other reasons.
return address. It is necessary to do this directly instead of using a
software breakpoint because the code used in processing that breakpoint
could itself be kprobe'd and cause a problematic reentry into the debug
exception handler.
Signed-off-by: William Cohen <wcohen@xxxxxxxxxx>
Signed-off-by: David A. Long <dave.long@xxxxxxxxxx>
---
arch/arm64/include/asm/kprobes.h | 1 +
arch/arm64/kernel/kprobes-arm64.h | 41 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/kprobes.c | 26 +++++++++++++++++++++++++
3 files changed, 68 insertions(+)
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index af31c4d..d081f49 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -58,5 +58,6 @@ int kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data);
int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr);
int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr);
+void kretprobe_trampoline(void);
#endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h
index ff8a55f..bdcfa62 100644
--- a/arch/arm64/kernel/kprobes-arm64.h
+++ b/arch/arm64/kernel/kprobes-arm64.h
@@ -27,4 +27,45 @@ extern kprobes_pstate_check_t * const kprobe_condition_checks[16];
enum kprobe_insn __kprobes
arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi);
+#define SAVE_REGS_STRING\
+ " stp x0, x1, [sp, #16 * 0]\n" \
+ " stp x2, x3, [sp, #16 * 1]\n" \
+ " stp x4, x5, [sp, #16 * 2]\n" \
+ " stp x6, x7, [sp, #16 * 3]\n" \
+ " stp x8, x9, [sp, #16 * 4]\n" \
+ " stp x10, x11, [sp, #16 * 5]\n" \
+ " stp x12, x13, [sp, #16 * 6]\n" \
+ " stp x14, x15, [sp, #16 * 7]\n" \
+ " stp x16, x17, [sp, #16 * 8]\n" \
+ " stp x18, x19, [sp, #16 * 9]\n" \
+ " stp x20, x21, [sp, #16 * 10]\n" \
+ " stp x22, x23, [sp, #16 * 11]\n" \
+ " stp x24, x25, [sp, #16 * 12]\n" \
+ " stp x26, x27, [sp, #16 * 13]\n" \
+ " stp x28, x29, [sp, #16 * 14]\n" \
+ " str x30, [sp, #16 * 15]\n" \
+ " mrs x0, nzcv\n" \
+ " str x0, [sp, #8 * 33]\n"
+
+
+#define RESTORE_REGS_STRING\
+ " ldr x0, [sp, #8 * 33]\n" \
+ " msr nzcv, x0\n" \
+ " ldp x0, x1, [sp, #16 * 0]\n" \
+ " ldp x2, x3, [sp, #16 * 1]\n" \
+ " ldp x4, x5, [sp, #16 * 2]\n" \
+ " ldp x6, x7, [sp, #16 * 3]\n" \
+ " ldp x8, x9, [sp, #16 * 4]\n" \
+ " ldp x10, x11, [sp, #16 * 5]\n" \
+ " ldp x12, x13, [sp, #16 * 6]\n" \
+ " ldp x14, x15, [sp, #16 * 7]\n" \
+ " ldp x16, x17, [sp, #16 * 8]\n" \
+ " ldp x18, x19, [sp, #16 * 9]\n" \
+ " ldp x20, x21, [sp, #16 * 10]\n" \
+ " ldp x22, x23, [sp, #16 * 11]\n" \
+ " ldp x24, x25, [sp, #16 * 12]\n" \
+ " ldp x26, x27, [sp, #16 * 13]\n" \
+ " ldp x28, x29, [sp, #16 * 14]\n" \
+ " ldr x30, [sp, #16 * 15]\n"
+
#endif /* _ARM_KERNEL_KPROBES_ARM64_H */
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index 6255814..570218c 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -560,6 +560,32 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
return 0;
}
+/*
+ * When a retprobed function returns, this code saves registers and
+ * calls trampoline_handler() runs, which calls the kretprobe's handler.
+ */
+static void __used __kprobes kretprobe_trampoline_holder(void)
+{
+ asm volatile (".global kretprobe_trampoline\n"
+ "kretprobe_trampoline:\n"
+ "sub sp, sp, %0\n"
+ SAVE_REGS_STRING
+ "mov x0, sp\n"
+ "bl trampoline_probe_handler\n"
+ /* Replace trampoline address in lr with actual
+ orig_ret_addr return address. */
+ "str x0, [sp, #16 * 15]\n"
+ RESTORE_REGS_STRING
+ "add sp, sp, %0\n"
+ "ret\n"
+ : : "I"(sizeof(struct pt_regs)) : "memory");
+}
+
+static void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
+{
+ return (void *) 0;
+}
+
int __init arch_init_kprobes(void)
{
return 0;
--
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