On 08/07/2018 01:20 PM, George Dunlap wrote: > On Mon, Aug 6, 2018 at 8:10 PM, Chris Brannon <c...@prgmr.com> wrote: >> I just got the following patch from a colleague. It's a backport of >> the XSA 274 kernel patch to 4.9.x kernels. The kernel patch given in >> the XSA would not apply cleanly. Would someone mind reviewing it? It >> would be much appreciated. >> >> commit b3681dd548d06deb2e1573890829dff4b15abf46 upstream. >> >> This version applies to v4.9. >> >> error_entry and error_exit communicate the user vs kernel status of >> the frame using %ebx. This is unnecessary -- the information is in >> regs->cs. Just use regs->cs. >> >> This makes error_entry simpler and makes error_exit more robust. >> >> It also fixes a nasty bug. Before all the Spectre nonsense, The >> xen_failsafe_callback entry point returned like this: >> >> ALLOC_PT_GPREGS_ON_STACK >> SAVE_C_REGS >> SAVE_EXTRA_REGS >> ENCODE_FRAME_POINTER >> jmp error_exit >> >> And it did not go through error_entry. This was bogus: RBX >> contained garbage, and error_exit expected a flag in RBX. >> Fortunately, it generally contained *nonzero* garbage, so the >> correct code path was used. As part of the Spectre fixes, code was >> added to clear RBX to mitigate certain speculation attacks. Now, >> depending on kernel configuration, RBX got zeroed and, when running >> some Wine workloads, the kernel crashes. This was introduced by: >> >> commit 3ac6d8c787b8 ("x86/entry/64: Clear registers for >> exceptions/interrupts, to reduce speculation attack surface") >> >> With this patch applied, RBX is no longer needed as a flag, and the >> problem goes away. >> >> Cc: Brian Gerst <brge...@gmail.com> >> Cc: Borislav Petkov <b...@alien8.de> >> Cc: Dominik Brodowski <li...@dominikbrodowski.net> >> Cc: Ingo Molnar <mi...@redhat.com> >> Cc: "H. Peter Anvin" <h...@zytor.com> >> Cc: Thomas Gleixner <t...@linutronix.de> >> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com> >> Cc: Juergen Gross <jgr...@suse.com> >> Cc: xen-devel@lists.xenproject.org >> Cc: x...@kernel.org >> Cc: sta...@vger.kernel.org >> Cc: Andy Lutomirski <l...@kernel.org> >> Fixes: 3ac6d8c787b8 ("x86/entry/64: Clear registers for >> exceptions/interrupts, to reduce speculation attack surface") >> Reported-and-tested-by: "M. Vefa Bicakci" <m....@runbox.com> >> Signed-off-by: Sarah Newman <s...@prgmr.com> > I think you need to retain Andy's SoB, and add your own underneath. > > This looks plausible to me -- Andy / Boris, any opinions?
LGTM. Note also that Andy's patch had slightly longer commit message (including some of the tags that you are missing), with this suggestion: [ Note to stable maintainers: this should probably get applied to all kernels. If you're nervous about that, a more conservative fix to add xorl %ebx,%ebx; incl %ebx before the jump to error_exit should also fix the problem. ] -boris _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel