@@ -20,6 +20,14 @@
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>
+enum kunwind_source {
+ KUNWIND_SOURCE_UNKNOWN,
+ KUNWIND_SOURCE_FRAME,
+ KUNWIND_SOURCE_CALLER,
+ KUNWIND_SOURCE_TASK,
+ KUNWIND_SOURCE_REGS_PC,
+};
+
/*
* Kernel unwind state
*
@@ -37,6 +45,7 @@ struct kunwind_state {
#ifdef CONFIG_KRETPROBES
struct llist_node *kr_cur;
#endif
+ enum kunwind_source source;
};
static __always_inline void
@@ -45,6 +54,7 @@ kunwind_init(struct kunwind_state *state,
{
unwind_init_common(&state->common);
state->task = task;
+ state->source = KUNWIND_SOURCE_UNKNOWN;
}
/*
@@ -62,6 +72,7 @@ kunwind_init_from_regs(struct kunwind_state *state,
state->common.fp = regs->regs[29];
state->common.pc = regs->pc;
+ state->source = KUNWIND_SOURCE_REGS_PC;
}
/*
@@ -79,6 +90,7 @@ kunwind_init_from_caller(struct kunwind_state *state)
state->common.fp = (unsigned long)__builtin_frame_address(1);
state->common.pc = (unsigned long)__builtin_return_address(0);
+ state->source = KUNWIND_SOURCE_CALLER;
}
/*
@@ -99,6 +111,7 @@ kunwind_init_from_task(struct kunwind_state *state,
state->common.fp = thread_saved_fp(task);
state->common.pc = thread_saved_pc(task);
+ state->source = KUNWIND_SOURCE_TASK;
}
static __always_inline int
@@ -148,9 +161,19 @@ kunwind_next(struct kunwind_state *state)
if (fp == (unsigned long)&task_pt_regs(tsk)->stackframe)
return -ENOENT;
- err = unwind_next_frame_record(&state->common);
- if (err)
- return err;
+ switch (state->source) {
+ case KUNWIND_SOURCE_FRAME:
+ case KUNWIND_SOURCE_CALLER:
+ case KUNWIND_SOURCE_TASK:
+ case KUNWIND_SOURCE_REGS_PC:
+ err = unwind_next_frame_record(&state->common);
+ if (err)
+ return err;
+ state->source = KUNWIND_SOURCE_FRAME;
+ break;
+ default:
+ return -EINVAL;
+ }
state->common.pc = ptrauth_strip_kernel_insn_pac(state->common.pc);
@@ -294,10 +317,26 @@ noinline noinstr void arch_bpf_stack_walk(bool (*consume_entry)(void *cookie, u6
kunwind_stack_walk(arch_bpf_unwind_consume_entry, &data, current, NULL);
}
+static const char *state_source_string(const struct kunwind_state *state)
+{
+ switch (state->source) {
+ case KUNWIND_SOURCE_FRAME: return NULL;
+ case KUNWIND_SOURCE_CALLER: return "C";
+ case KUNWIND_SOURCE_TASK: return "T";
+ case KUNWIND_SOURCE_REGS_PC: return "P";
+ default: return "U";
+ }
+}
+
static bool dump_backtrace_entry(const struct kunwind_state *state, void *arg)
{
+ const char *source = state_source_string(state);
char *loglvl = arg;
- printk("%s %pSb\n", loglvl, (void *)state->common.pc);
+ printk("%s %pSb%s%s%s\n", loglvl,
+ (void *)state->common.pc,
+ source ? " (" : "",
+ source ? source : "",
+ source ? ")" : "");
return true;
}
When analysing a stacktrace it can be useful to know where an unwound PC came from, as in some situations certain sources may be suspect or known to be unreliable. In future it would also be useful to track this so that certain unwind steps can be performed in a stateful manner. For example when unwinding across an exception boundary, we'd ideally unwind pt_regs::pc, then pt_regs::lr, then the next frame record. This patch adds an enumerated set of unwind sources, tracks this during the unwind, and updates dump_backtrace() to log these for interesting unwind steps. The interesting sources recorded are: "C" - the PC came from the caller of an unwind function. "T" - the PC came from thread_saved_pc() for a blocked task. "P" - the PC came from a pt_regs::pc. "U" - the PC came from an unknown source (indicates an unwinder error). ... with nothing recorded when the PC came from a frame_record::pc as this is the vastly common case and logging this would make it difficult to spot the more interesting cases. For example, when triggering a backtrace via magic-sysrq + L, the CPU handling the sysrq will have a backtrace whose first element is the caller (C) of dump_backtrace(): | Call trace: | show_stack+0x18/0x30 (C) | dump_stack_lvl+0x60/0x80 | dump_stack+0x18/0x24 | nmi_cpu_backtrace+0xfc/0x140 | ... ... and other CPUs will have a backtrace whose first element is their pt_regs::pc (P) at the instant the backtrace IPI was taken: | Call trace: | _raw_spin_unlock_irqrestore+0x8/0x50 (P) | wake_up_process+0x18/0x24 | process_timeout+0x14/0x20 | call_timer_fn.isra.0+0x24/0x80 | ... Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Josh Poimboeuf <jpoimboe@kernel.org> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Mark Brown <broonie@kernel.org> Cc: Miroslav Benes <mbenes@suse.cz> Cc: Puranjay Mohan <puranjay12@gmail.com> Cc: Will Deacon <will@kernel.org> --- arch/arm64/kernel/stacktrace.c | 47 +++++++++++++++++++++++++++++++--- 1 file changed, 43 insertions(+), 4 deletions(-)