Messages in this thread | | | Date | Mon, 21 Jun 2021 16:29:21 +0200 | From | Borislav Petkov <> | Subject | Re: FAILED: patch "[PATCH] x86/fpu: Invalidate FPU state after a failed XRSTOR from a" failed to apply to 5.4-stable tree |
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On Mon, Jun 21, 2021 at 12:51:46PM +0200, gregkh@linuxfoundation.org wrote: > > The patch below does not apply to the 5.4-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <stable@vger.kernel.org>. > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From d8778e393afa421f1f117471144f8ce6deb6953a Mon Sep 17 00:00:00 2001 > From: Andy Lutomirski <luto@kernel.org> > Date: Tue, 8 Jun 2021 16:36:19 +0200 > Subject: [PATCH] x86/fpu: Invalidate FPU state after a failed XRSTOR from a > user buffer > > Both Intel and AMD consider it to be architecturally valid for XRSTOR to > fail with #PF but nonetheless change the register state. The actual > conditions under which this might occur are unclear [1], but it seems > plausible that this might be triggered if one sibling thread unmaps a page > and invalidates the shared TLB while another sibling thread is executing > XRSTOR on the page in question. > > __fpu__restore_sig() can execute XRSTOR while the hardware registers > are preserved on behalf of a different victim task (using the > fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but > modify the registers. > > If this happens, then there is a window in which __fpu__restore_sig() > could schedule out and the victim task could schedule back in without > reloading its own FPU registers. This would result in part of the FPU > state that __fpu__restore_sig() was attempting to load leaking into the > victim task's user-visible state. > > Invalidate preserved FPU registers on XRSTOR failure to prevent this > situation from corrupting any state. > > [1] Frequent readers of the errata lists might imagine "complex > microarchitectural conditions". > > Fixes: 1d731e731c4c ("x86/fpu: Add a fastpath to __fpu__restore_sig()") > Signed-off-by: Andy Lutomirski <luto@kernel.org> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Borislav Petkov <bp@suse.de> > Acked-by: Dave Hansen <dave.hansen@linux.intel.com> > Acked-by: Rik van Riel <riel@surriel.com> > Cc: stable@vger.kernel.org > Link: https://lkml.kernel.org/r/20210608144345.758116583@linutronix.de > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index d5bc96a536c2..4ab9aeb9a963 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -369,6 +369,25 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > fpregs_unlock(); > return 0; > } > + > + /* > + * The above did an FPU restore operation, restricted to > + * the user portion of the registers, and failed, but the > + * microcode might have modified the FPU registers > + * nevertheless. > + * > + * If the FPU registers do not belong to current, then > + * invalidate the FPU register state otherwise the task might > + * preempt current and return to user space with corrupted > + * FPU registers. > + * > + * In case current owns the FPU registers then no further > + * action is required. The fixup below will handle it > + * correctly. > + */ > + if (test_thread_flag(TIF_NEED_FPU_LOAD)) > + __cpu_invalidate_fpregs_state(); > + > fpregs_unlock(); > } else {
So I'm looking at this and 5.4.127 has:
if (!ret) { fpregs_mark_activate(); fpregs_unlock(); return 0; } fpregs_deactivate(fpu); <--- fpregs_unlock();
i.e., an unconditional fpu invalidation there. Which got removed by:
98265c17efa9 ("x86/fpu/xstate: Preserve supervisor states for the slow path in __fpu__restore_sig()")
in 5.7.
so that Fixes: commit above which points to a 5.1 kernel is probably wrong-ish.
amluto?
-- Regards/Gruss, Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
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