[PATCH v8 5/7] arm64: Add trampoline code for kretprobes

David Long
2015-08-11T00:53:34Z

From: William Cohen <wcohen@redhat.com>

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 original saved caller
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@redhat.com>
Signed-off-by: David A. Long <dave.long@linaro.org>
---
arch/arm64/include/asm/kprobes.h | 2 ++
arch/arm64/kernel/Makefile | 1 +
arch/arm64/kernel/asm-offsets.c | 22 ++++++++++++
arch/arm64/kernel/kprobes.c | 5 +++
arch/arm64/kernel/kprobes_trampoline.S | 61 ++++++++++++++++++++++++++++++++++
5 files changed, 91 insertions(+)
create mode 100644 arch/arm64/kernel/kprobes_trampoline.S

diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index af31c4d..83399aa 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -58,5 +58,7 @@ 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);
+void __kprobes *trampoline_probe_handler(struct pt_regs *regs);

#endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 5e9d54f..75d5fb0 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -33,6 +33,7 @@ arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o
arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o
arm64-obj-$(CONFIG_KGDB) += kgdb.o
arm64-obj-$(CONFIG_KPROBES) += kprobes.o kprobes-arm64.o \
+ kprobes_trampoline.o \
probes-simulate-insn.o \
probes-condn-check.o
arm64-obj-$(CONFIG_EFI) += efi.o efi-stub.o efi-entry.o
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index c99701a..475c93b 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -49,6 +49,28 @@ int main(void)
DEFINE(S_X5, offsetof(struct pt_regs, regs[5]));
DEFINE(S_X6, offsetof(struct pt_regs, regs[6]));
DEFINE(S_X7, offsetof(struct pt_regs, regs[7]));
+ DEFINE(S_X8, offsetof(struct pt_regs, regs[8]));
+ DEFINE(S_X9, offsetof(struct pt_regs, regs[9]));
+ DEFINE(S_X10, offsetof(struct pt_regs, regs[10]));
+ DEFINE(S_X11, offsetof(struct pt_regs, regs[11]));
+ DEFINE(S_X12, offsetof(struct pt_regs, regs[12]));
+ DEFINE(S_X13, offsetof(struct pt_regs, regs[13]));
+ DEFINE(S_X14, offsetof(struct pt_regs, regs[14]));
+ DEFINE(S_X15, offsetof(struct pt_regs, regs[15]));
+ DEFINE(S_X16, offsetof(struct pt_regs, regs[16]));
+ DEFINE(S_X17, offsetof(struct pt_regs, regs[17]));
+ DEFINE(S_X18, offsetof(struct pt_regs, regs[18]));
+ DEFINE(S_X19, offsetof(struct pt_regs, regs[19]));
+ DEFINE(S_X20, offsetof(struct pt_regs, regs[20]));
+ DEFINE(S_X21, offsetof(struct pt_regs, regs[21]));
+ DEFINE(S_X22, offsetof(struct pt_regs, regs[22]));
+ DEFINE(S_X23, offsetof(struct pt_regs, regs[23]));
+ DEFINE(S_X24, offsetof(struct pt_regs, regs[24]));
+ DEFINE(S_X25, offsetof(struct pt_regs, regs[25]));
+ DEFINE(S_X26, offsetof(struct pt_regs, regs[26]));
+ DEFINE(S_X27, offsetof(struct pt_regs, regs[27]));
+ DEFINE(S_X28, offsetof(struct pt_regs, regs[28]));
+ DEFINE(S_X29, offsetof(struct pt_regs, regs[29]));
DEFINE(S_LR, offsetof(struct pt_regs, regs[30]));
DEFINE(S_SP, offsetof(struct pt_regs, sp));
#ifdef CONFIG_COMPAT
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index 6255814..98db85c 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -560,6 +560,11 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
return 0;
}

+void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
+{
+ return (void *) 0;
+}
+
int __init arch_init_kprobes(void)
{
return 0;
diff --git a/arch/arm64/kernel/kprobes_trampoline.S b/arch/arm64/kernel/kprobes_trampoline.S
new file mode 100644
index 0000000..dd0172b
--- /dev/null
+++ b/arch/arm64/kernel/kprobes_trampoline.S
@@ -0,0 +1,61 @@
+/*
+ * trampoline entry and return code for kretprobes.
+ */
+
+#include <linux/linkage.h>
+#include <generated/asm-offsets.h>
+
+ .text
+
+ENTRY(kretprobe_trampoline)
+
+ sub sp, sp, #S_FRAME_SIZE
+
+ stp x0, x1, [sp, #S_X0]
+ stp x2, x3, [sp, #S_X2]
+ stp x4, x5, [sp, #S_X4]
+ stp x6, x7, [sp, #S_X6]
+ stp x8, x9, [sp, #S_X8]
+ stp x10, x11, [sp, #S_X10]
+ stp x12, x13, [sp, #S_X12]
+ stp x14, x15, [sp, #S_X14]
+ stp x16, x17, [sp, #S_X16]
+ stp x18, x19, [sp, #S_X18]
+ stp x20, x21, [sp, #S_X20]
+ stp x22, x23, [sp, #S_X22]
+ stp x24, x25, [sp, #S_X24]
+ stp x26, x27, [sp, #S_X26]
+ stp x28, x29, [sp, #S_X28]
+ str x30, [sp, #S_LR]
+ mrs x0, nzcv
+ str x0, [sp, #S_PSTATE]
+
+ mov x0, sp
+ bl trampoline_probe_handler
+ /* Replace trampoline address in lr with actual
+ orig_ret_addr return address. */
+ str x0, [sp, #S_LR]
+
+ ldr x0, [sp, #S_PSTATE]
+ msr nzcv, x0
+ ldp x0, x1, [sp, #S_X0]
+ ldp x2, x3, [sp, #S_X2]
+ ldp x4, x5, [sp, #S_X4]
+ ldp x6, x7, [sp, #S_X6]
+ ldp x8, x9, [sp, #S_X8]
+ ldp x10, x11, [sp, #S_X10]
+ ldp x12, x13, [sp, #S_X12]
+ ldp x14, x15, [sp, #S_X14]
+ ldp x16, x17, [sp, #S_X16]
+ ldp x18, x19, [sp, #S_X18]
+ ldp x20, x21, [sp, #S_X20]
+ ldp x22, x23, [sp, #S_X22]
+ ldp x24, x25, [sp, #S_X24]
+ ldp x26, x27, [sp, #S_X26]
+ ldp x28, x29, [sp, #S_X28]
+ ldr x30, [sp, #S_LR]
+
+ add sp, sp, #S_FRAME_SIZE
+ ret
+
+ENDPROC(kretprobe_trampoline)
--
1.8.1.2