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Message-ID: <4dd594ad-490a-68ee-9e32-fbd9f135bd54@intel.com> Date: Wed, 21 Sep 2022 13:59:06 -0700 From: Dave Hansen <dave.hansen@...el.com> To: Guenter Roeck <linux@...ck-us.net>, Peter Zijlstra <peterz@...radead.org> Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, keescook@...omium.org, Sean Christopherson <seanjc@...gle.com> Subject: Re: [PATCH v2] x86/mm: Refuse W^X violations On 9/21/22 13:07, Guenter Roeck wrote: > [ 2.042861] CPA refuse W^X violation: 8000000000000063 -> 0000000000000063 range: 0x00000000c00a0000 - 0x00000000c00a0fff PFN a0 > ILLOPC: cbc65efa: 0f 0b > [ 2.043267] WARNING: CPU: 0 PID: 1 at arch/x86/mm/pat/set_memory.c:600 __change_page_attr_set_clr+0xdca/0xdd0 ... > [ 2.050307] ---[ end trace 0000000000000000 ]--- > [ 2.050762] PCI: PCI BIOS area is rw and x. Use pci=nobios if you want it NX. > [ 2.051115] kernel tried to execute NX-protected page - exploit attempt? (uid: 0) > [ 2.051115] BUG: unable to handle page fault for address: c00fd2bf This _looks_ like it is working as intended. The PCI BIOS code tried to make a RWX page. The CPA code refused to do it and presumably returned an error, leaving a RW page, non-executable page. The PCI code didn't check the set_memory_x() return code and tried to go execute anyway. That resulted in the oops. I was able to reproduce this pretty easily. The workaround from dmesg is pci=nobios. That seems to do the trick for me, although that advise was sandwiched between a warning and an oops, so not the easiest to find. I'm a bit torn what to do on this one. Breaking the boot is bad, but so is leaving RWX memory around. Thoughts?
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