perf: Fix unsafe frame rewinding with hot regs fetching
When we fetch the hot regs and rewind to the nth caller, it might happen that we dereference a frame pointer outside the kernel stack boundaries, like in this example: perf_trace_sched_switch+0xd5/0x120 schedule+0x6b5/0x860 retint_careful+0xd/0x21 Since we directly dereference a userspace frame pointer here while rewinding behind retint_careful, this may end up in a crash. Fix this by simply using probe_kernel_address() when we rewind the frame pointer. This issue will have a much more proper fix in the next version of the perf_arch_fetch_caller_regs() API that will only need to rewind to the first caller. Reported-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Tested-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Miller <davem@davemloft.net> Cc: Archs <linux-arch@vger.kernel.org>
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@ -14,6 +14,8 @@
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#define get_bp(bp) asm("movq %%rbp, %0" : "=r" (bp) :)
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#endif
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#include <linux/uaccess.h>
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extern void
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show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
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unsigned long *stack, unsigned long bp, char *log_lvl);
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@ -42,8 +44,10 @@ static inline unsigned long rewind_frame_pointer(int n)
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get_bp(frame);
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#ifdef CONFIG_FRAME_POINTER
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while (n--)
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frame = frame->next_frame;
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while (n--) {
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if (probe_kernel_address(&frame->next_frame, frame))
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break;
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}
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#endif
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return (unsigned long)frame;
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