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powerpc/livepatch: relax reliable stack tracer checks for first-frame

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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: df78d3f614 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model")
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Joe Lawrence 2019-01-22 10:57:22 -05:00 committed by Michael Ellerman
parent a50d3250d7
commit 18be37603d
1 changed files with 24 additions and 8 deletions
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32
arch/powerpc/kernel/stacktrace.c
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@ -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;