Re: [PATCH 7/9] x86/mm: Shadow stack page fault error checking
From: Andy Lutomirski <luto@kernel.org>
Date: 2018-06-07 16:26:57
Also in:
linux-arch, linux-mm, lkml
On Thu, Jun 7, 2018 at 7:40 AM Yu-cheng Yu [off-list ref] wrote:
If a page fault is triggered by a shadow stack access (e.g. call/ret) or shadow stack management instructions (e.g. wrussq), then bit[6] of the page fault error code is set. In access_error(), we check if a shadow stack page fault is within a shadow stack memory area. Signed-off-by: Yu-cheng Yu <redacted>
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 73bd8c95ac71..2b3b9170109c 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c@@ -1166,6 +1166,17 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) (error_code & X86_PF_INSTR), foreign)) return 1; + /* + * Verify X86_PF_SHSTK is within a shadow stack VMA. + * It is always an error if there is a shadow stack + * fault outside a shadow stack VMA. + */ + if (error_code & X86_PF_SHSTK) { + if (!(vma->vm_flags & VM_SHSTK)) + return 1; + return 0; + } +
What, if anything, would go wrong without this change? It seems like it might be purely an optimization. If so, can you mention that in the comment? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html