lkml.org 
[lkml]   [2018]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] x86/pkeys: Explicitly treat PK #PF on kernel address as a bad area
From
Date


> 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?
\
 
 \ /
  Last update: 2018-08-31 05:10    [W:0.069 / U:10.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site