[PATCH v6 4/8] seccomp: add __NR_seccomp_* aliases for rt_sigreturn and clone/fork

[Cong Wang <xiyou.wangcong@gmail.com>]

From: Cong Wang <cwang@multikernel.io>

The existing __NR_seccomp_* aliases name only the strict-mode syscalls
(read/write/exit/sigreturn). SEND_REDIRECT must also recognise
rt_sigreturn and the clone/fork task-creation family, native and compat,
so it can refuse to redirect them.

Gate these behind a new SECCOMP_ARCH_REDIRECT opt-in, mirroring how
SECCOMP_ARCH_NATIVE gates the bitmap cache: an arch declares it only once
it supplies a complete, verified set of these numbers, and where it is
undefined the feature is compiled out. This avoids a generic fallback
silently handing an arch a wrong number that would drop a syscall from
the deny list. x86_64 opts in and supplies the ia32 compat numbers.

Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Cong Wang <cwang@multikernel.io>
---
 arch/x86/include/asm/seccomp.h | 15 ++++++++++++++-
 include/asm-generic/seccomp.h  | 30 ++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/seccomp.h b/arch/x86/include/asm/seccomp.h
index 42bcd42d70d1..a911fce504ac 100644
--- a/arch/x86/include/asm/seccomp.h
+++ b/arch/x86/include/asm/seccomp.h
@@ -6,6 +6,7 @@
 
 #ifdef CONFIG_X86_32
 #define __NR_seccomp_sigreturn		__NR_sigreturn
+#define __NR_seccomp_rt_sigreturn	__NR_rt_sigreturn
 #endif
 
 #ifdef CONFIG_COMPAT
@@ -14,12 +15,18 @@
 #define __NR_seccomp_write_32		__NR_ia32_write
 #define __NR_seccomp_exit_32		__NR_ia32_exit
 #define __NR_seccomp_sigreturn_32	__NR_ia32_sigreturn
+#define __NR_seccomp_rt_sigreturn_32	__NR_ia32_rt_sigreturn
+#define __NR_seccomp_clone_32		__NR_ia32_clone
+#define __NR_seccomp_clone3_32		__NR_ia32_clone3
+#define __NR_seccomp_fork_32		__NR_ia32_fork
+#define __NR_seccomp_vfork_32		__NR_ia32_vfork
 #endif
 
 #ifdef CONFIG_X86_64
 # define SECCOMP_ARCH_NATIVE		AUDIT_ARCH_X86_64
 # define SECCOMP_ARCH_NATIVE_NR		NR_syscalls
 # define SECCOMP_ARCH_NATIVE_NAME	"x86_64"
+# define SECCOMP_ARCH_REDIRECT		1
 # ifdef CONFIG_COMPAT
 #  define SECCOMP_ARCH_COMPAT		AUDIT_ARCH_I386
 #  define SECCOMP_ARCH_COMPAT_NR	IA32_NR_syscalls
@@ -28,8 +35,14 @@
 /*
  * x32 will have __X32_SYSCALL_BIT set in syscall number. We don't support
  * caching them and they are treated as out of range syscalls, which will
- * always pass through the BPF filter.
+ * always pass through the BPF filter. It shares AUDIT_ARCH_X86_64 with the
+ * native ABI, so refuse to redirect it: the generic denylist keys off plain
+ * syscall numbers and cannot name x32's sigreturn/clone.
  */
+static inline bool arch_seccomp_redirect_deny(const struct seccomp_data *sd)
+{
+	return sd->nr & __X32_SYSCALL_BIT;
+}
 #else /* !CONFIG_X86_64 */
 # define SECCOMP_ARCH_NATIVE		AUDIT_ARCH_I386
 # define SECCOMP_ARCH_NATIVE_NR	        NR_syscalls
diff --git a/include/asm-generic/seccomp.h b/include/asm-generic/seccomp.h
index 6b6f42bc58f9..42b1b9b79ddf 100644
--- a/include/asm-generic/seccomp.h
+++ b/include/asm-generic/seccomp.h
@@ -26,6 +26,36 @@
 #define __NR_seccomp_sigreturn		__NR_rt_sigreturn
 #endif
 
+#ifdef SECCOMP_ARCH_REDIRECT
+#ifndef __NR_seccomp_rt_sigreturn
+#define __NR_seccomp_rt_sigreturn	__NR_seccomp_sigreturn
+#endif
+#ifndef __NR_seccomp_clone
+#define __NR_seccomp_clone		__NR_clone
+#endif
+#ifndef __NR_seccomp_clone3
+#ifdef __NR_clone3
+#define __NR_seccomp_clone3		__NR_clone3
+#else
+#define __NR_seccomp_clone3		(-1)
+#endif
+#endif
+#ifndef __NR_seccomp_fork
+#ifdef __NR_fork
+#define __NR_seccomp_fork		__NR_fork
+#else
+#define __NR_seccomp_fork		(-1)
+#endif
+#endif
+#ifndef __NR_seccomp_vfork
+#ifdef __NR_vfork
+#define __NR_seccomp_vfork		__NR_vfork
+#else
+#define __NR_seccomp_vfork		(-1)
+#endif
+#endif
+#endif /* SECCOMP_ARCH_REDIRECT */
+
 #ifdef CONFIG_COMPAT
 #ifndef get_compat_mode1_syscalls
 static inline const int *get_compat_mode1_syscalls(void)
-- 
2.43.0