Re: [PATCH 0/7] ARM: support THREAD_INFO_IN_TASK (v3)

[Ard Biesheuvel <ardb@kernel.org>]

On Wed, 8 Sept 2021 at 09:01, Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
>
> On 08/09/2021 00:00, Keith Packard wrote:
> > Placing thread_info in the kernel stack leaves it vulnerable to stack
> > overflow attacks. This short series addresses that by using the
> > existing THREAD_INFO_IN_TASK infrastructure.
> >
> > This is the third version of this series, in this version the changes
> > are restricted to hardware which provides the TPIDRPRW register. This
> > register is repurposed from holding the per_cpu_offset value to
> > holding the 'current' value as that allows fetching this value
> > atomically so that it can be used in a preemptable context.
> >
> > The series is broken into seven pieces:
> >
> >  1) Change the secondary_start_kernel API to receive the cpu
> >     number. This avoids needing to be able to find this value independently in
> >     future patches.
> >
> >  2) Change the secondary_start_kernel API to also receive the 'task'
> >     value. Passing the value to this function also avoids needing to
> >     be able to discover it independently.
> >
> >  3) A cleanup which avoids assuming that THREAD_INFO_IN_TASK is not set.
> >
> >  4) A hack, borrowed from the powerpc arch, which allows locating the 'cpu'
> >     field in either thread_info or task_struct, without requiring linux/sched.h
> >     to be included in asm/smp.h
> >
> >  5) Disable the optimization storing per_cpu_offset in TPIDRPRW. This leaves
> >     the register free to hold 'current' instead.
> >
> >  6) Use TPIDRPRW for 'current'. This is enabled for either CPU_V6K or CPU_V7,
> >     but not if CPU_V6 is also enabled.
> >
> >  7) Enable THREAD_INFO_IN_TASK whenever TPIDRPRW is used to hold 'current'.
>
> Hi,
>
> Thanks for your patches. This seems to be a v3 but the patches are not
> marked with it. Use "-v3" in format-patch to get it right.
>
> The email here also lacks diffstat which is useful, for example to check
> whether any maintainer's relevant files are touched here. You can get it
> with "--cover-letter".
>
> In total the command should look like:
>     git format-patch --cover-letter -v3 -7 HEAD
>
> Of course you can use any other tools to achieve the same result but as
> of now - result is not the same.
>

Also, this ended up in my GMail spam folder, likely due to some
antispam ID header being set incorrectly?