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    SubjectRe: [PATCH] x86, 32-bit: Fix invalid stack address while in softirq
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    On Thu, 2012-09-06 at 17:02 +0200, Robert Richter wrote:

    > > > --- a/arch/x86/oprofile/backtrace.c
    > > > +++ b/arch/x86/oprofile/backtrace.c
    > > > @@ -113,7 +113,7 @@ x86_backtrace(struct pt_regs * const regs, unsigned int depth)
    > > >
    > > > if (!user_mode_vm(regs)) {
    > > > unsigned long stack = kernel_stack_pointer(regs);
    > > > - if (depth)
    > > > + if (depth & stack)
    > >
    > > Can other users of kernel_stack_pointer() be nailed by a return of NULL?
    >
    > It would be save here too, but dump_trace() falls back to the current
    > stack in case there is no stack address given which we don't want with
    > oprofile.
    >
    > I was looking at all users of kernel_stack_pointer() and could not
    > find any direct pointer dereference of the sp. The only potential
    > problems I found could arise here:
    >
    > arch/x86/kernel/kprobes.c:resume_execution()
    > arch/x86/kernel/time.c:profile_pc()
    >
    > It is not quite clear if we really need code here that checks the
    > pointer. Since a NULL pointer access has the same effect as if the
    > stack address would be wrong which would be the case without the
    > patch, I rather tend not to change the code here.

    Then a comment should be in the oprofile code too. Something to the
    effect that oprofile is special and can cause kernel_stack_pointer() to
    return NULL in some cases, thus we need to check for it.

    -- Steve




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