On Tue, Feb 11, 2025 at 2:20 AM John Paul Adrian Glaubitz
<glaubitz@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On Tue, 2025-02-04 at 23:35 +0100, Ivan Kokshaysky wrote:
> > This series fixes oopses on Alpha/SMP observed since kernel v6.9. [1]
> > Thanks to Magnus Lindholm for identifying that remarkably longstanding
> > bug.
> >
> > The problem is that GCC expects 16-byte alignment of the incoming stack
> > since early 2004, as Maciej found out [2]:
> > Having actually dug speculatively I can see that the psABI was changed in
> > GCC 3.5 with commit e5e10fb4a350 ("re PR target/14539 (128-bit long double
> > improperly aligned)") back in Mar 2004, when the stack pointer alignment
> > was increased from 8 bytes to 16 bytes, and arch/alpha/kernel/entry.S has
> > various suspicious stack pointer adjustments, starting with SP_OFF which
> > is not a whole multiple of 16.
> >
> > Also, as Magnus noted, "ALPHA Calling Standard" [3] required the same:
> > D.3.1 Stack Alignment
> > This standard requires that stacks be octaword aligned at the time a
> > new procedure is invoked.
> >
> > However:
> > - the "normal" kernel stack is always misaligned by 8 bytes, thanks to
> > the odd number of 64-bit words in 'struct pt_regs', which is the very
> > first thing pushed onto the kernel thread stack;
> > - syscall, fault, interrupt etc. handlers may, or may not, receive aligned
> > stack depending on numerous factors.
> >
> > Somehow we got away with it until recently, when we ended up with
> > a stack corruption in kernel/smp.c:smp_call_function_single() due to
> > its use of 32-byte aligned local data and the compiler doing clever
> > things allocating it on the stack.
> >
> > Patche 1 is preparatory; 2 - the main fix; 3 - fixes remaining
> > special cases.
> >
> > Ivan.
> >
> > [1] https://lore.kernel.org/rcu/CA+=Fv5R9NG+1SHU9QV9hjmavycHKpnNyerQ=Ei90G98ukRcRJA@xxxxxxxxxxxxxx/#r
> > [2] https://lore.kernel.org/rcu/alpine.DEB.2.21.2501130248010.18889@xxxxxxxxxxxxxxxxx/
> > [3] https://bitsavers.org/pdf/dec/alpha/Alpha_Calling_Standard_Rev_2.0_19900427.pdf
> > ---
> > Changes in v2:
> > - patch #1: provide empty 'struct pt_regs' to fix compile failure in libbpf,
> > reported by John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>;
> > update comment and commit message accordingly;
> > - cc'ed <stable@xxxxxxxxxxxxxxx> as older kernels ought to be fixed as well.
> >
> > Changes in v3:
> > - patch #1 dropped for the time being;
> > - updated commit messages as Maciej suggested.
> > ---
> > Ivan Kokshaysky (3):
> > alpha: replace hardcoded stack offsets with autogenerated ones
> > alpha: make stack 16-byte aligned (most cases)
> > alpha: align stack for page fault and user unaligned trap handlers
> >
> > arch/alpha/include/uapi/asm/ptrace.h | 2 ++
> > arch/alpha/kernel/asm-offsets.c | 4 ++++
> > arch/alpha/kernel/entry.S | 24 ++++++++++--------------
> > arch/alpha/kernel/traps.c | 2 +-
> > arch/alpha/mm/fault.c | 4 ++--
> > 5 files changed, 19 insertions(+), 17 deletions(-)
>
> Can we get this landed this week, maybe for v6.14-rc3? This way it will quickly
> backported to various stable kernels which means it will reach Debian unstable
> within a few days.
>
> Thanks,
> Adrian
Yeah, I'll vacuum the patches up and send them to Linus.
I've been running them on my ES47 and while my ES47 is still unstable,
these patches definitely solve this bug [1] and fix failures I saw
with the rcu_torture module!
Thanks a bunch to all of you!
[1] https://bugzilla.kernel.org/show_bug.cgi?id=213143
