ACK: [SRU][I][PATCH 0/1] s390x: prevent unreachable jumps with new gcc

[Tim Gardner]

Acked-by: Tim Gardner <tim.gardner at canonical.com>

On 2/2/22 8:00 AM, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1954676
> 
> [Impact]
> 
> We have experienced a nasty kernel bug in Jammy on s390x, starting with
> gcc 11.2.0-10ubuntu1: the object files generated with the new gcc could
> contain unreachable jumps causing kernel panics at runtime, because the
> kernel can jump to random addresses in memory.
> 
> This has been fixed in Jammy by reverting this patch in gcc:
> [1] https://gcc.gnu.org/git/?p=gcc.git;a=patch;h=2335aa8771acd06b082d3e15d9f21ae0a802afd7
> 
> In addition to that recently a kernel fix also landed upstream:
> 
>    f3b7e73b2c66 ("s390/module: fix loading modules with a lot of relocations")
> 
> This fix has been applied to the Jammy kernel already.
> 
> We should probably apply this fix to the Impish kernel as well, in case
> the same gcc patch lands in Impish.
> 
> [Test case]
> 
> Build zfs on s390x with a gcc that includes the patch mentioned above
> [1], try to insmod zfs.ko and you should experience random kernel
> panics.
> 
> [Fix]
> 
> Apply upstream commit:
> 
>    f3b7e73b2c66 ("s390/module: fix loading modules with a lot of relocations")
> 
> [Regression potential]
> 
> This patch affects the code that takes care of loading external kernel
> modules (.ko) on s390x, so we may see regressions on s390x when some
> kernel modules are loaded. However this change has been applied uptream
> and tested extensively on the affected architecture, so regression
> potential should be minimal.
> 
> 

-- 
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Tim Gardner
Canonical, Inc