From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
Date: Tue, 20 Nov 2018 09:13:39 +0100 [thread overview]
Message-ID: <20181120081339.GA35948@gmail.com> (raw)
In-Reply-To: <20181120073925.GC79825@gmail.com>
* Ingo Molnar <mingo@kernel.org> wrote:
>
> * Andy Lutomirski <luto@kernel.org> wrote:
>
> > The fault handling code tries to validate that a page fault from
> > user mode that would extend the stack is within a certain range of
> > the user SP. regs->sp is only equal to the user SP if
> > user_mode(regs). In the extremely unlikely event that that
> > sw_error_code had the USER bit set but the faulting instruction was
> > in the kernel (i.e. the faulting instruction was WRUSS), then the
> > *kernel* stack pointer would have been checked, which would be an
> > info leak.
> >
> > Note to -stable maintainers: don't backport this unless you backport
> > CET. The bug it fixes is unobservable in current kernels.
> >
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > ---
> > arch/x86/mm/fault.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 91d4d2722f2e..eae7ee3ce89b 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> > bad_area(regs, sw_error_code, address);
> > return;
> > }
> > - if (sw_error_code & X86_PF_USER) {
> > + if (user_mode(regs)) {
> > /*
> > * Accessing the stack below %sp is always a bug.
> > * The large cushion allows instructions like enter
>
> Note that this check is gone now due to:
>
> 1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
>
> Thanks,
Ok, I like your series - I have applied the first ~7 patches of it to
tip:x86/mm, the rest is interacting with 1d8ca3be86eb - will apply the
rest as well once you send a v2.
Thanks,
Ingo
next prev parent reply other threads:[~2018-11-20 8:13 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 22:45 [PATCH 00/13] x86/fault: #PF improvements, mostly related to USER bit Andy Lutomirski
2018-11-19 22:45 ` [PATCH 01/13] x86/fault: Check user_mode(regs) when avoiding an mmap_sem deadlock Andy Lutomirski
2018-11-20 8:14 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-20 8:15 ` [PATCH 01/13] " Peter Zijlstra
2018-11-19 22:45 ` [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension Andy Lutomirski
2018-11-20 7:39 ` Ingo Molnar
2018-11-20 8:13 ` Ingo Molnar [this message]
2018-11-19 22:45 ` [PATCH 03/13] x86/cpufeatures, x86/fault: Mark SMAP as disabled when configured out Andy Lutomirski
2018-11-20 8:15 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 04/13] x86/fault: Fold smap_violation() into do_user_addr_fault() Andy Lutomirski
2018-11-20 8:15 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 05/13] x86/fault: Fix SMAP #PF handling buglet for implicit supervisor accesses Andy Lutomirski
2018-11-20 8:16 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 06/13] x86/fault: Improve the condition for signalling vs OOPSing Andy Lutomirski
2018-11-20 8:16 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 07/13] x86/fault: Make error_code sanitization more robust Andy Lutomirski
2018-11-20 8:17 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 08/13] x86/fault: Don't set thread.cr2, etc before OOPSing Andy Lutomirski
2018-11-20 8:17 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 09/13] x86/fault: Remove sw_error_code Andy Lutomirski
2018-11-19 22:45 ` [PATCH 10/13] x86/fault: Don't try to recover from an implicit supervisor access Andy Lutomirski
2018-11-19 22:45 ` [PATCH 11/13] x86/oops: Show the correct CS value in show_regs() Andy Lutomirski
2018-11-19 22:45 ` [PATCH 12/13] x86/fault: Decode page fault OOPSes better Andy Lutomirski
2018-11-27 14:46 ` Sean Christopherson
2018-11-19 22:45 ` [PATCH 13/13] x86/vsyscall/64: Use X86_PF constants in the simulated #PF error code Andy Lutomirski
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