Commit 18be3760 authored by Joe Lawrence's avatar Joe Lawrence Committed by Michael Ellerman
Browse files

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: df78d3f6 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model")
Signed-off-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent a50d3250

arch/powerpc/kernel/stacktrace.c

+24 −8
Original line number Diff line number Diff line
@@ -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;

CRA Git | Maintained and supported by SUSTech CRA and CCSE