Messages in this thread | | | Subject | Re: [PATCH] x86/pkeys: Explicitly treat PK #PF on kernel address as a bad area | From | Andy Lutomirski <> | Date | Thu, 30 Aug 2018 20:08:10 -0700 |
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> On Aug 30, 2018, at 7:38 PM, Jann Horn <jannh@google.com> wrote: > >> On Tue, 7 Aug 2018 Dave Hansen <dave.hansen@intel.com> wrote: >> >>> On 08/07/2018 10:29 AM, Sean Christopherson wrote: >>> if (unlikely(fault_in_kernel_space(address))) { >>> + /* >>> + * We should never encounter a protection keys fault on a >>> + * kernel address as kernel address are always mapped with >>> + * _PAGE_USER=0, i.e. PKRU isn't enforced. >>> + */ >>> + if (WARN_ON_ONCE(error_code & X86_PF_PK)) >>> + goto bad_kernel_address; >> >> I just realized one more thing: the vsyscall page can bite us here. >> It's at a fault_in_kernel_space() address and we *can* trigger a pkey >> fault on it if we jump to an instruction that reads from a >> pkey-protected area. >> >> We can make a gadget out of unaligned vsyscall instructions that does >> that. See: >> >> 0xffffffffff600002: shlb $0x0,0x0(%rax) >> >> Then, we turn off access to all pkeys, including pkey-0, then jump to >> the unaligned vsyscall instruction, which reads %rax, which is a kernel >> address: > > Andy got rid of the (native) vsyscall page in > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=076ca272a14cea558b1092ec85cea08510283f2a > ('x86/vsyscall/64: Drop "native" vsyscalls') a few months ago, right? > At this point, the vsyscall page should never be executable.
Indeed.
Can one of you cc me on the original patch?
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