From 18be37603de81674e41a0b0282326a0debc1696e Mon Sep 17 00:00:00 2001 From: Joe Lawrence Date: Tue, 22 Jan 2019 10:57:22 -0500 Subject: [PATCH] powerpc/livepatch: relax reliable stack tracer checks for first-frame The bottom-most stack frame (the first to be unwound) may be largely uninitialized, for the "Power Architecture 64-Bit ELF V2 ABI" only requires its backchain pointer to be set. The reliable stack tracer should be careful when verifying this frame: skip checks on STACK_FRAME_LR_SAVE and STACK_FRAME_MARKER offsets that may contain uninitialized residual data. Fixes: df78d3f61480 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model") Signed-off-by: Joe Lawrence Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/stacktrace.c | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c index e2c50b5..06688f4 100644 --- a/arch/powerpc/kernel/stacktrace.c +++ b/arch/powerpc/kernel/stacktrace.c @@ -84,6 +84,12 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) EXPORT_SYMBOL_GPL(save_stack_trace_regs); #ifdef CONFIG_HAVE_RELIABLE_STACKTRACE +/* + * This function returns an error if it detects any unreliable features of the + * stack. Otherwise it guarantees that the stack trace is reliable. + * + * If the task is not 'current', the caller *must* ensure the task is inactive. + */ int save_stack_trace_tsk_reliable(struct task_struct *tsk, struct stack_trace *trace) @@ -142,12 +148,6 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk, if (sp & 0xF) return 1; - /* Mark stacktraces with exception frames as unreliable. */ - if (sp <= stack_end - STACK_INT_FRAME_SIZE && - stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) { - return 1; - } - newsp = stack[0]; /* Stack grows downwards; unwinder may only go up. */ if (newsp <= sp) @@ -158,11 +158,26 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk, return 1; /* invalid backlink, too far up. */ } + /* + * We can only trust the bottom frame's backlink, the + * rest of the frame may be uninitialized, continue to + * the next. + */ + if (firstframe) { + firstframe = 0; + goto next; + } + + /* Mark stacktraces with exception frames as unreliable. */ + if (sp <= stack_end - STACK_INT_FRAME_SIZE && + stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) { + return 1; + } + /* Examine the saved LR: it must point into kernel code. */ ip = stack[STACK_FRAME_LR_SAVE]; - if (!firstframe && !__kernel_text_address(ip)) + if (!__kernel_text_address(ip)) return 1; - firstframe = 0; /* * FIXME: IMHO these tests do not belong in @@ -183,6 +198,7 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk, else trace->skip--; +next: if (newsp == stack_end) break; -- 2.7.4