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SubjectRe: [PATCH 06/11] x86/fault: Improve kernel-executing-user-memory handling
On Sun, Jan 31, 2021 at 09:24:37AM -0800, Andy Lutomirski wrote:
> Right now we treat the case of the kernel trying to execute from user
> memory more or less just like the kernel getting a page fault on a user
> access. In the failure path, we check for erratum #93, try to otherwise
> fix up the error, and then oops.
> If we manage to jump to the user address space, with or without SMEP, we
> should not try to resolve the page fault. This is an error, pure and
> simple. Rearrange the code so that we catch this case early, check for
> erratum #93, and bail out.

And I'm scratching my head why are you talking about kernel trying
to execute from user memory but doh, that erratum truncates the high
32-bits of rIP and the #PF address looks like a user address but
X86_PF_USER is clear.



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