Re: [PATCH 5/8] arm64: Recover kretprobe modified return address in stacktrace
From: Mark Rutland <mark.rutland@arm.com>
Date: 2021-10-13 10:14:00
Also in:
lkml
On Fri, Oct 08, 2021 at 09:28:58PM +0900, Masami Hiramatsu wrote:
quoted hunk ↗ jump to hunk
Since the kretprobe replaces the function return address with the kretprobe_trampoline on the stack, stack unwinder shows it instead of the correct return address. This checks whether the next return address is the __kretprobe_trampoline(), and if so, try to find the correct return address from the kretprobe instance list. With this fix, now arm64 can enable CONFIG_ARCH_CORRECT_STACKTRACE_ON_KRETPROBE, and pass the kprobe self tests. Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/stacktrace.h | 2 ++ arch/arm64/kernel/stacktrace.c | 3 +++ 3 files changed, 6 insertions(+)diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 5c7ae4c3954b..edde5171ffb2 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig@@ -11,6 +11,7 @@ config ARM64 select ACPI_PPTT if ACPI select ARCH_HAS_DEBUG_WX select ARCH_BINFMT_ELF_STATE + select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION select ARCH_ENABLE_MEMORY_HOTPLUG select ARCH_ENABLE_MEMORY_HOTREMOVEdiff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 8aebc00c1718..8f997a602651 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h@@ -9,6 +9,7 @@ #include <linux/sched.h> #include <linux/sched/task_stack.h> #include <linux/types.h> +#include <linux/llist.h> #include <asm/memory.h> #include <asm/ptrace.h>@@ -59,6 +60,7 @@ struct stackframe { #ifdef CONFIG_FUNCTION_GRAPH_TRACER int graph; #endif + struct llist_node *kr_cur;
As with the fgraph bits above, please make this depedn on the relevant Kconfig, i.e. | #ifdef CONFIG_KRETPROBES | struct llist_node *kr_cur; | #endif
quoted hunk ↗ jump to hunk
}; extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index 8982a2b78acf..f1eef5745542 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c@@ -129,6 +129,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) frame->pc = ret_stack->ret; } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ + if (is_kretprobe_trampoline(frame->pc)) + frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
Please ifdef this, like the CONFIG_FUNCTION_GRAPH_TRACER bits above. i.e. | #ifdef CONFIG_KRETPROBES | if (is_kretprobe_trampoline(frame->pc)) | frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur); | #endif What does kretprobe_find_ret_addr() do when it can't find the original address? I couldn't spot it in this series or in mainline. As a future thing, I'd like to be able to have monotonicity and completeness checks as part of the unwind, i.e. checking that we consume the kretprobe address *in-order*, and can identify whether we've skipped any, so that we can identify when unwinding has gone wrong. Does it do that today? It'd be nice if it could signal failure reliably (without causing a BUG() or similar), e.g. by returning an error code.
quoted hunk ↗ jump to hunk
frame->pc = ptrauth_strip_insn_pac(frame->pc);@@ -224,6 +226,7 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, { struct stackframe frame; + memset(&frame, 0, sizeof(frame));
Please initialise stackframe::kr_cur in start_backtrace, where we initialize all the other fields in struct stackframe, i.e. just after the CONFIG_FUNCTION_GRAPH_TRACER bit, have: | #ifdef CONFIG_KRETPROBES | frame->kr_cur = NULL; | #endif Thanks, Mark.
if (regs) start_backtrace(&frame, regs->regs[29], regs->pc); else if (task == current)
_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel