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authorSandeepa Prabhu <sandeepa.prabhu@linaro.org>2014-12-22 23:49:01 -0500
committerSteve Capper <steve.capper@linaro.org>2015-01-27 16:46:18 +0000
commit3e6e8fbe737362df6e628bff6308bba66c293799 (patch)
treeef557cb14a529e972ab3703108c66a264b0653b6 /arch
parent961229d73097beabc13e151dd674dd3a7888e618 (diff)
downloadlinux-3e6e8fbe737362df6e628bff6308bba66c293799.tar.gz
arm64: Add kernel return probes support(kretprobes)
AArch64 ISA does not have instructions to pop the PC register value from the stack(like ARM v7 has ldmia {...,pc}) without using one of the general purpose registers. This means return probes cannot return to the actual return address directly without modifying register context, and without trapping into debug exception. So, like many other architectures, we prepare a global routine with NOPs which serve as a trampoline to hack away the function return address by placing an extra kprobe on the trampoline entry. The pre-handler of this special 'trampoline' kprobe executes the return probe handler functions and restores original return address in ELR_EL1. This way the saved pt_regs still hold the original register context to be carried back to the probed kernel function. Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org> Signed-off-by: David A. Long <dave.long@linaro.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/Kconfig1
-rw-r--r--arch/arm64/include/asm/kprobes.h1
-rw-r--r--arch/arm64/kernel/kprobes.c114
3 files changed, 115 insertions, 1 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b3f61bae55f..de4f0561cd1 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -68,6 +68,7 @@ config ARM64
select HAVE_RCU_TABLE_FREE
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_KPROBES if !XIP_KERNEL
+ select HAVE_KRETPROBES if HAVE_KPROBES
select IRQ_DOMAIN
select MODULES_USE_ELF_RELA
select NO_BOOTMEM
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index b35d3b9d29f..a2de3b8359b 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -56,5 +56,6 @@ void arch_remove_kprobe(struct kprobe *);
int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
int kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data);
+void kretprobe_trampoline(void);
#endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index 31a7894ec43..cd1069cdaa9 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -559,6 +559,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
return 0;
}
+/*
+ * Kretprobes: kernel return probes handling
+ *
+ * AArch64 mode does not support popping the PC value from the
+ * stack like on ARM 32-bit (ldmia {..,pc}), so atleast one
+ * register need to be used to achieve branching/return.
+ * It means return probes cannot return back to the original
+ * return address directly without modifying the register context.
+ *
+ * So like other architectures, we prepare a global routine
+ * with NOPs, which serve as trampoline address that hack away the
+ * function return, with the exact register context.
+ * Placing a kprobe on trampoline routine entry will trap again to
+ * execute return probe handlers and restore original return address
+ * in ELR_EL1, this way saved pt_regs still hold the original
+ * register values to be carried back to the caller.
+ */
+static void __used kretprobe_trampoline_holder(void)
+{
+ asm volatile (".global kretprobe_trampoline\n"
+ "kretprobe_trampoline:\n"
+ "NOP\n\t"
+ "NOP\n\t");
+}
+
+static int __kprobes
+trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+ struct kretprobe_instance *ri = NULL;
+ struct hlist_head *head, empty_rp;
+ struct hlist_node *tmp;
+ unsigned long flags, orig_ret_addr = 0;
+ unsigned long trampoline_address =
+ (unsigned long)&kretprobe_trampoline;
+
+ INIT_HLIST_HEAD(&empty_rp);
+ kretprobe_hash_lock(current, &head, &flags);
+
+ /*
+ * It is possible to have multiple instances associated with a given
+ * task either because multiple functions in the call path have
+ * a return probe installed on them, and/or more than one return
+ * probe was registered for a target function.
+ *
+ * We can handle this because:
+ * - instances are always inserted at the head of the list
+ * - when multiple return probes are registered for the same
+ * function, the first instance's ret_addr will point to the
+ * real return address, and all the rest will point to
+ * kretprobe_trampoline
+ */
+ hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+ if (ri->task != current)
+ /* another task is sharing our hash bucket */
+ continue;
+
+ if (ri->rp && ri->rp->handler) {
+ __this_cpu_write(current_kprobe, &ri->rp->kp);
+ get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+ ri->rp->handler(ri, regs);
+ __this_cpu_write(current_kprobe, NULL);
+ }
+
+ orig_ret_addr = (unsigned long)ri->ret_addr;
+ recycle_rp_inst(ri, &empty_rp);
+
+ if (orig_ret_addr != trampoline_address)
+ /*
+ * This is the real return address. Any other
+ * instances associated with this task are for
+ * other calls deeper on the call stack
+ */
+ break;
+ }
+
+ kretprobe_assert(ri, orig_ret_addr, trampoline_address);
+ /* restore the original return address */
+ instruction_pointer(regs) = orig_ret_addr;
+ reset_current_kprobe();
+ kretprobe_hash_unlock(current, &flags);
+
+ hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+ hlist_del(&ri->hlist);
+ kfree(ri);
+ }
+
+ kprobes_restore_local_irqflag(regs);
+
+ /* return 1 so that post handlers not called */
+ return 1;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+ struct pt_regs *regs)
+{
+ ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
+
+ /* replace return addr (x30) with trampoline */
+ regs->regs[30] = (long)&kretprobe_trampoline;
+}
+
+static struct kprobe trampoline = {
+ .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
+ .pre_handler = trampoline_probe_handler
+};
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+ return p->addr == (kprobe_opcode_t *) &kretprobe_trampoline;
+}
+
/* Break Handler hook */
static struct break_hook kprobes_break_hook = {
.esr_mask = BRK64_ESR_MASK,
@@ -576,5 +687,6 @@ int __init arch_init_kprobes(void)
register_break_hook(&kprobes_break_hook);
register_step_hook(&kprobes_step_hook);
- return 0;
+ /* register trampoline for kret probe */
+ return register_kprobe(&trampoline);
}