Messages in this thread | | | Date | Fri, 3 May 2019 08:04:34 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails |
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On Thu, May 02, 2019 at 07:11:39PM +0200, Sebastian Andrzej Siewior wrote: > In the compacted form, XSAVES may save only the XMM+SSE state but skip > FP (x87 state). > > This is denoted by header->xfeatures = 6. The fastpath > (copy_fpregs_to_sigframe()) does that but _also_ initialises the FP > state (cwd to 0x37f, mxcsr as we do, remaining fields to 0). > > The slowpath (copy_xstate_to_user()) leaves most of the FP > state untouched. Only mxcsr and mxcsr_flags are set due to > xfeatures_mxcsr_quirk(). Now that XFEATURE_MASK_FP is set > unconditionally, see > > 04944b793e18 ("x86: xsave: set FP, SSE bits in the xsave header in the user sigcontext"), > > on return from the signal, random garbage is loaded as the FP state. > > Instead of utilizing copy_xstate_to_user(), fault-in the user memory > and retry the fast path. Ideally, the fast path succeeds on the second > attempt but may be retried again if the memory is swapped out due > to memory pressure. If the user memory can not be faulted-in then > get_user_pages() returns an error so we don't loop forever. > > Fault in memory via get_user_pages_unlocked() so > copy_fpregs_to_sigframe() succeeds without a fault. > > Fixes: 69277c98f5eef ("x86/fpu: Always store the registers in copy_fpstate_to_sigframe()") > Reported-by: Kurt Kanzenbach <kurt.kanzenbach@linutronix.de> > Suggested-by: Dave Hansen <dave.hansen@intel.com> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > v1…v2: > - s/get_user_pages()/get_user_pages_unlocked()/ > - merge cleanups > > I'm posting this all-in-one fix up replacing the original patch so we > don't have a merge window with known bugs (that is the one that the > patch was going the fix and the KASAN fallout that it introduced). > > arch/x86/kernel/fpu/signal.c | 31 +++++++++++++++---------------- > 1 file changed, 15 insertions(+), 16 deletions(-)
Queued to tip:WIP.x86/fpu for some hammering ontop ...
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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