Re: [PATCH v2] x86/mm: Refuse W^X violations
From: Pavel Machek
Date: Sun Oct 02 2022 - 06:34:11 EST
On Wed 2022-09-21 13:59:06, Dave Hansen wrote:
> 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.
Well, the original patch is bad. Boot regressions are not acceptable.
We should first add an WARN_ON(), debug and fix the failures, then we
can start refusing the transitions.
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