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=Ei90G98ukRc... [2] https://lore.kernel.org/rcu/alpine.DEB.2.21.2501130248010.18889@angie.orcam.... [3] https://bitsavers.org/pdf/dec/alpha/Alpha_Calling_Standard_Rev_2.0_19900427.... --- Changes in v2: - patch #1: provide empty 'struct pt_regs' to fix compile failure in libbpf, reported by John Paul Adrian Glaubitz glaubitz@physik.fu-berlin.de; update comment and commit message accordingly; - cc'ed stable@vger.kernel.org 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(-)