From e21555436f196c241503c7c6240272e57783235c Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Tue, 1 Mar 2016 11:41:33 -0800 Subject: [PATCH] x86/mm/pkeys: Fix access_error() denial of writes to write-only VMA Andrey Wagin reported that a simple test case was broken by: 2b5f7d013fc ("mm/core, x86/mm/pkeys: Add execute-only protection keys support") This test case creates an unreadable VMA and my patch assumed that all writes must be to readable VMAs. The simplest fix for this is to remove the pkey-related bits in access_error(). For execute-only support, I believe the existing version is sufficient because the permissions we are trying to enforce are entirely expressed in vma->vm_flags. We just depend on pkeys to get *an* exception, it does not matter that PF_PK was set, or even what state PKRU is in. I will re-add the necessary bits with the full pkeys implementation that includes the new syscalls. The three cases that matter are: 1. If a write to an execute-only VMA occurs, we will see PF_WRITE set, but !VM_WRITE on the VMA, and return 1. All execute-only VMAs have VM_WRITE clear by definition. 2. If a read occurs on a present PTE, we will fall in to the "read, present" case and return 1. 3. If a read occurs to a non-present PTE, we will miss the "read, not present" case, because the execute-only VMA will have VM_EXEC set, and we will properly return 0 allowing the PTE to be populated. Test program: int main() { int *p; p = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); p[0] = 1; return 0; } Reported-by: Andrey Wagin , Signed-off-by: Dave Hansen Acked-by: Kirill A. Shutemov Cc: Dave Hansen Cc: Kirill A. Shutemov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-mm@kvack.org Cc: linux-next@vger.kernel.org Fixes: 62b5f7d013fc ("mm/core, x86/mm/pkeys: Add execute-only protection keys support") Link: http://lkml.kernel.org/r/20160301194133.65D0110C@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- arch/x86/mm/fault.c | 18 ------------------ 1 file changed, 18 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 5877b92ab6f1..6138db471b17 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1100,24 +1100,6 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) { /* This is only called for the current mm, so: */ bool foreign = false; - /* - * Access or read was blocked by protection keys. We do - * this check before any others because we do not want - * to, for instance, confuse a protection-key-denied - * write with one for which we should do a COW. - */ - if (error_code & PF_PK) - return 1; - - if (!(error_code & PF_INSTR)) { - /* - * Assume all accesses require either read or execute - * permissions. This is not an instruction access, so - * it requires read permissions. - */ - if (!(vma->vm_flags & VM_READ)) - return 1; - } /* * Make sure to check the VMA so that we do not perform * faults just to hit a PF_PK as soon as we fill in a -- 2.20.1