This is a note to let you know that I've just added the patch titled
x86/entry/64: Clear extra registers beyond syscall arguments, to reduce speculation attack surface
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-entry-64-clear-extra-registers-beyond-syscall-arguments-to-reduce-speculation-attack-surface.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Mon Feb 26 20:55:53 CET 2018
From: Dan Williams dan.j.williams@intel.com Date: Fri, 23 Feb 2018 14:06:21 -0800 Subject: x86/entry/64: Clear extra registers beyond syscall arguments, to reduce speculation attack surface To: gregkh@linuxfoundation.org Cc: Andi Kleen ak@linux.intel.com, Denys Vlasenko dvlasenk@redhat.com, Peter Zijlstra peterz@infradead.org, Brian Gerst brgerst@gmail.com, "H. Peter Anvin" hpa@zytor.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Borislav Petkov bp@alien8.de, Andy Lutomirski luto@kernel.org, Josh Poimboeuf jpoimboe@redhat.com, Thomas Gleixner tglx@linutronix.de, Linus Torvalds torvalds@linux-foundation.org, Ingo Molnar mingo@kernel.org Message-ID: 151942358116.21775.14209781084277174517.stgit@dwillia2-desk3.amr.corp.intel.com
From: Dan Williams dan.j.williams@intel.com
commit 8e1eb3fa009aa7c0b944b3c8b26b07de0efb3200 upstream.
At entry userspace may have (maliciously) populated the extra registers outside the syscall calling convention with arbitrary values that could be useful in a speculative execution (Spectre style) attack.
Clear these registers to minimize the kernel's attack surface.
Note, this only clears the extra registers and not the unused registers for syscalls less than 6 arguments, since those registers are likely to be clobbered well before their values could be put to use under speculation.
Note, Linus found that the XOR instructions can be executed with minimized cost if interleaved with the PUSH instructions, and Ingo's analysis found that R10 and R11 should be included in the register clearing beyond the typical 'extra' syscall calling convention registers.
Suggested-by: Linus Torvalds torvalds@linux-foundation.org Reported-by: Andi Kleen ak@linux.intel.com Signed-off-by: Dan Williams dan.j.williams@intel.com Cc: stable@vger.kernel.org Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/151787988577.7847.16733592218894189003.stgit@dwilli... [ Made small improvements to the changelog and the code comments. ] Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/entry/entry_64.S | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -176,13 +176,26 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) pushq %r8 /* pt_regs->r8 */ pushq %r9 /* pt_regs->r9 */ pushq %r10 /* pt_regs->r10 */ + /* + * Clear extra registers that a speculation attack might + * otherwise want to exploit. Interleave XOR with PUSH + * for better uop scheduling: + */ + xorq %r10, %r10 /* nospec r10 */ pushq %r11 /* pt_regs->r11 */ + xorq %r11, %r11 /* nospec r11 */ pushq %rbx /* pt_regs->rbx */ + xorl %ebx, %ebx /* nospec rbx */ pushq %rbp /* pt_regs->rbp */ + xorl %ebp, %ebp /* nospec rbp */ pushq %r12 /* pt_regs->r12 */ + xorq %r12, %r12 /* nospec r12 */ pushq %r13 /* pt_regs->r13 */ + xorq %r13, %r13 /* nospec r13 */ pushq %r14 /* pt_regs->r14 */ + xorq %r14, %r14 /* nospec r14 */ pushq %r15 /* pt_regs->r15 */ + xorq %r15, %r15 /* nospec r15 */
/* IRQs are off. */ movq %rsp, %rdi
Patches currently in stable-queue which might be from dan.j.williams@intel.com are
queue-4.9/mm-fix-devm_memremap_pages-collision-handling.patch queue-4.9/ib-core-disable-memory-registration-of-filesystem-dax-vmas.patch queue-4.9/mm-avoid-spurious-bad-pmd-warning-messages.patch queue-4.9/mm-introduce-get_user_pages_longterm.patch queue-4.9/mm-fail-get_vaddr_frames-for-filesystem-dax-mappings.patch queue-4.9/fs-dax.c-fix-inefficiency-in-dax_writeback_mapping_range.patch queue-4.9/device-dax-implement-split-to-catch-invalid-munmap-attempts.patch queue-4.9/v4l2-disable-filesystem-dax-mapping-support.patch queue-4.9/libnvdimm-dax-fix-1gb-aligned-namespaces-vs-physical-misalignment.patch queue-4.9/x86-entry-64-clear-extra-registers-beyond-syscall-arguments-to-reduce-speculation-attack-surface.patch queue-4.9/libnvdimm-fix-integer-overflow-static-analysis-warning.patch