From: Magnus Lindholm <linmag7@gmail.com>
To: richard.henderson@linaro.org, mattst88@gmail.com,
linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org
Cc: linmag7@gmail.com
Subject: [PATCH 03/14] alpha: preserve rolled-back registers for SIGSYS
Date: Tue, 3 Nov 2026 22:35:09 +0100 [thread overview]
Message-ID: <20261103214120.1099893-4-linmag7@gmail.com> (raw)
In-Reply-To: <20261103214120.1099893-1-linmag7@gmail.com>
Record syscall_rollback() in syscall_meta so skipped-syscall handling
preserves r0 and a3. Otherwise seccomp RET_TRAP handlers and kill-action
core dumps lose the original syscall number and fourth argument.
Fixes: 83bd31c2840b ("alpha: enable GENERIC_ENTRY")
Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
arch/alpha/include/asm/syscall.h | 4 +++-
arch/alpha/include/asm/thread_info.h | 1 +
arch/alpha/kernel/signal.c | 12 ++++++++++--
3 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/alpha/include/asm/syscall.h b/arch/alpha/include/asm/syscall.h
index c1394910f584f9ca42367ffc33b1c0ac46cfe112..22315b932f854a71fd3babf6565dda443c6c7a77 100644
--- a/arch/alpha/include/asm/syscall.h
+++ b/arch/alpha/include/asm/syscall.h
@@ -105,14 +105,16 @@ static inline void syscall_set_return_value(struct task_struct *task,
}
}
-/* Restore the original syscall nr after seccomp/ptrace modified regs->r1. */
+/* Preserve the original syscall registers for a skipped syscall. */
static inline void syscall_rollback(struct task_struct *task,
struct pt_regs *regs)
{
unsigned long nr = task_thread_info(task)->syscall_saved_nr;
+ regs->r0 = nr;
regs->r1 = nr;
+ task_thread_info(task)->syscall_meta |= ALPHA_SYSCALL_META_ROLLBACK;
}
static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h
index d781ac79106dd1178b9cb0e094333139db531bed..49bc08f3b5a98fbcb1d4ac919001bf70c3db614b 100644
--- a/arch/alpha/include/asm/thread_info.h
+++ b/arch/alpha/include/asm/thread_info.h
@@ -57,6 +57,7 @@ register unsigned long *current_stack_pointer __asm__ ("$30");
#define ALPHA_SYSCALL_META_SKIP 0x2
#define ALPHA_SYSCALL_META_FORCE_SUCCESS 0x4
+#define ALPHA_SYSCALL_META_ROLLBACK 0x10
/*
* Thread information flags:
diff --git a/arch/alpha/kernel/signal.c b/arch/alpha/kernel/signal.c
index 441d8dd61055d5ddc321c2221984eab8aca5d206..3fae37b4593f22f07a375ab7bc0b0712d0130a07 100644
--- a/arch/alpha/kernel/signal.c
+++ b/arch/alpha/kernel/signal.c
@@ -587,10 +587,11 @@ alpha_syscall_enter_select(struct pt_regs *regs, long syscall)
* entry work did not already change the return state.
*/
if (unlikely(!permit || (unsigned long)nr >= NR_syscalls)) {
- if (regs->r0 == saved_r0 && regs->r19 == saved_r19)
+ if (!(ti->syscall_meta & ALPHA_SYSCALL_META_ROLLBACK) &&
+ regs->r0 == saved_r0 && regs->r19 == saved_r19)
syscall_set_return_value(current, regs, -ENOSYS, 0);
- ti->syscall_meta = ALPHA_SYSCALL_META_SKIP;
+ ti->syscall_meta |= ALPHA_SYSCALL_META_SKIP;
return fn; /* ignored by asm when SKIP is set */
}
@@ -617,6 +618,13 @@ alpha_finish_syscall_to_user_mode(struct pt_regs *regs, long ret)
instrumentation_begin();
+ if (meta & ALPHA_SYSCALL_META_ROLLBACK) {
+ ti->syscall_saved_nr = 0;
+ instrumentation_end();
+ syscall_exit_to_user_mode(regs);
+ return;
+ }
+
if (meta & ALPHA_SYSCALL_META_SKIP) {
/*
* Skip-dispatch path: ptrace/seccomp may already have installed
--
2.43.0
next prev parent reply other threads:[~2026-11-03 21:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-03 21:35 [PATCH 00/14] alpha: fix entry bugs and consolidate generic helpers Magnus Lindholm
2026-11-03 21:35 ` [PATCH 01/14] alpha: fix saved registers in page-fault oops dumps Magnus Lindholm
2026-11-03 21:35 ` [PATCH 02/14] alpha: report syscall errors correctly to audit Magnus Lindholm
2026-11-03 21:35 ` Magnus Lindholm [this message]
2026-11-03 21:35 ` [PATCH 04/14] alpha: fix syscall restart eligibility Magnus Lindholm
2026-11-03 21:35 ` [PATCH 05/14] alpha: distinguish skipped syscalls from invalid numbers Magnus Lindholm
2026-11-03 21:35 ` [PATCH 06/14] alpha: dispatch system calls from C Magnus Lindholm
2026-11-03 21:35 ` [PATCH 07/14] alpha: use generic entry helpers for interrupts and exceptions Magnus Lindholm
2026-11-03 21:35 ` [PATCH 08/14] alpha: use generic syscall exit for new tasks Magnus Lindholm
2026-11-03 21:35 ` [PATCH 09/14] alpha: remove obsolete core dump register hooks Magnus Lindholm
2026-11-03 21:35 ` [PATCH 10/14] alpha: use generic syscall audit classification Magnus Lindholm
2026-11-03 21:35 ` [PATCH 11/14] alpha: use generic ptrace memory writes Magnus Lindholm
2026-11-03 21:35 ` [PATCH 12/14] alpha: use memparse for memory size options Magnus Lindholm
2026-11-03 21:35 ` [PATCH 13/14] alpha: use generic getrusage for OSF resource accounting Magnus Lindholm
2026-11-03 21:35 ` [PATCH 14/14] alpha: use generic CPU device registration Magnus Lindholm
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