ACK/Cmnt: [SRU][Trusty][PULL] Prevent speculation on user controlled pointer (LP: #1775137)

[Stefan Bader]

On 28.06.2018 16:47, Juerg Haefliger wrote:
> BugLink: https://bugs.launchpad.net/bugs/1775137
> 
> == SRU Justification ==
> Upstream's Spectre v1 mitigation prevents speculation on a user controlled
> pointer. This part of the Spectre v1 patchset was never backported to 4.4 (for
> unknown reasons) so Xenial/Trusty/Precise are lacking it as well. All the other
> stable upstream kernels include it, so add it to our older kernels.
> 
> == Fix ==
> Backport the following patches:
> x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec
> x86/usercopy: Replace open coded stac/clac with __uaccess_{begin, end}
> x86: Introduce __uaccess_begin_nospec() and uaccess_try_nospec
> 
> == Regression Potential ==
> Low. Patches have been in upstream (and other distro kernels) for quite a while
> now and the changes only introduce a barrier on copy_from_user operations.
> 
> == Test Case ==
> TBD.
> 
> Compile-tested all supported architectures.
> 
> Signed-off-by: Juerg Haefliger <juergh at canonical.com>
> ---
> 
> The following changes since commit 182dabb3ee807633a0a11e8bbac93a64d111fdd3:
> 
>   UBUNTU: SAUCE: filter: Use barrier_nospec() instead of osb() (2018-06-28 16:08:50 +0200)
> 
> are available in the Git repository at:
> 
>   git://git.launchpad.net/~juergh/+git/trusty-linux lp1775137
> 
> for you to fetch changes up to 01c904cae0a339aeb07d383f9f46526f5467b096:
> 
>   x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec (2018-06-28 16:41:27 +0200)
> 
> ----------------------------------------------------------------
> Dan Williams (3):
>       x86: Introduce __uaccess_begin_nospec() and uaccess_try_nospec
>       x86/usercopy: Replace open coded stac/clac with __uaccess_{begin, end}
>       x86/uaccess: Use __uaccess_begin_nospec() and uaccess_try_nospec
> 
> Linus Torvalds (2):
>       x86: reorganize SMAP handling in user space accesses
>       x86: fix SMAP in 32-bit environments
> 
>  arch/x86/include/asm/uaccess.h    | 47 +++++++++++++++-----
>  arch/x86/include/asm/uaccess_32.h | 24 ++++++++++
>  arch/x86/include/asm/uaccess_64.h | 94 +++++++++++++++++++++++++++------------
>  arch/x86/lib/usercopy_32.c        | 20 ++++-----
>  4 files changed, 136 insertions(+), 49 deletions(-)
> 
Acked-by: Stefan Bader <stefan.bader at canonical.com>

Apart from not being able to always fully understand what is done things looked
to be according to was was said in the commit messages. Maybe the only thing I
was idly wondering was why half of it is backported from upstream and other
things taken from 3.16.y.

Of course this depends on the other pull request which I would hope gets re-sent
after cleaning up.

-Stefan

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