On Fri, Sep 18, 2020 at 9:42 AM Russell King - ARM Linux admin
[off-list ref] wrote:

On Thu, Sep 17, 2020 at 07:29:37PM +0200, Arnd Bergmann wrote:

quoted

On Tue, Sep 8, 2020 at 8:15 AM Christoph Hellwig [off-list ref] wrote:

I looked through the history now and the only code path I could
find that would arrive here this way is from bad_mode(), indicating
that there is probably a hardware bug or the contents of *regs are
corrupted.

Yes, that's correct.  It isn't something entirely theoretical, although
we never see it now, it used to happen in the distant past due to saved
regs corruption.  If bad_mode() ever gets called, all bets are off and
we're irrecoverably crashing.

Note that in that case, while user_mode(regs) may return true or false,
regs->ARM_sp and regs->ARM_lr are always the SVC mode stack and return
address after regs has been stacked, and not the expected values for
the parent context (which we have most likely long since destroyed.)

Ok, I have rewritten the patch and my changelog text accordingly, sending
an updated version now.

Thanks,

      Arnd

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