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SubjectRe: [PATCH 2/2] x86, perf: Optimize stack walk user accesses
On Mon, Oct 19, 2015 at 03:54:29PM -0700, Andi Kleen wrote:
> @@ -2307,7 +2312,13 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
> frame.next_frame = NULL;
> frame.return_address = 0;
>
> - bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
> + if (!access_ok(VERIFY_READ, fp, 16))
> + break;
> +
> + bytes = __copy_from_user_nmi(&frame.next_frame, fp, 8);
> + if (bytes != 0)
> + break;
> + bytes = __copy_from_user_nmi(&frame.return_address, fp+8, 8);
> if (bytes != 0)
> break;
>

The previous patch that introduces this function states that any caller
must have pagefault_disable() or be from interrupt context.

Perf can call this function from !interrupt context (imagine a
tracepoint or other software event), should we therefore not add a
pagefault_disable()/enable() pair around the entire while() loop?


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