Commit 55b22075 authored by Magnus Lindholm's avatar Magnus Lindholm
Browse files

alpha: add support for SECCOMP and SECCOMP_FILTER 



Add SECCOMP and SECCOMP_FILTER support to the Alpha architecture and fix
syscall entry and ptrace issues uncovered by the seccomp-bpf selftests.

The syscall entry path is reworked to consistently track syscall state
using r0, r1 and r2:
  - r1 holds the active syscall number
  - r2 preserves the original syscall number for restart
  - r0 carries the return value, with r19 (a3) indicating success/error

This allows syscall restarts to be permitted only for valid ERESTART*
return codes and prevents kernel-internal restart values from leaking to
userspace. The syscall tracing error marker is corrected to use the saved
syscall number slot, matching the Alpha ABI.

Additionally, implement minimal PTRACE_GETREGSET and PTRACE_SETREGSET
support for NT_PRSTATUS, exporting struct pt_regs directly. This fixes
ptrace-based seccomp tests that previously failed with -EIO.

With these changes, seccomp-bpf and ptrace syscall tests pass reliably on
Alpha.

Tested-by: default avatarMichael Cree <mcree@orcon.net.nz>
Signed-off-by: default avatarMagnus Lindholm <linmag7@gmail.com>
Link: https://lore.kernel.org/r/20260409171439.8759-2-linmag7@gmail.com


Signed-off-by: default avatarMagnus Lindholm <linmag7@gmail.com>
parent 6de23f81

Documentation/features/seccomp/seccomp-filter/arch-support.txt

+1 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 
    -----------------------

    |         arch |status|

    -----------------------

    |       alpha: | TODO |

    |       alpha: |  ok  |

    |         arc: | TODO |

    |         arm: |  ok  |

    |       arm64: |  ok  |

arch/alpha/Kconfig

+2 −0
Original line number Diff line number Diff line
@@ -31,6 +31,8 @@ config ALPHA 
	select GENERIC_SMP_IDLE_THREAD

	select HAS_IOPORT

	select HAVE_ARCH_AUDITSYSCALL

	select HAVE_ARCH_SECCOMP

	select HAVE_ARCH_SECCOMP_FILTER

	select HAVE_MOD_ARCH_SPECIFIC

	select LOCK_MM_AND_FIND_VMA

	select MODULES_USE_ELF_RELA

arch/alpha/include/asm/seccomp.h

0 → 100644
+13 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _ASM_ALPHA_SECCOMP_H

#define _ASM_ALPHA_SECCOMP_H



#include <asm/unistd.h>

#include <asm-generic/seccomp.h>

#include <uapi/linux/audit.h>



#define SECCOMP_ARCH_NATIVE            AUDIT_ARCH_ALPHA

#define SECCOMP_ARCH_NATIVE_NR         NR_syscalls

#define SECCOMP_ARCH_NATIVE_NAME       "alpha"



#endif /* _ASM_ALPHA_SECCOMP_H */

arch/alpha/include/asm/syscall.h

+89 −1
Original line number Diff line number Diff line
@@ -3,6 +3,10 @@ 
#define _ASM_ALPHA_SYSCALL_H



#include <uapi/linux/audit.h>

#include <linux/audit.h>

#include <linux/sched.h>

#include <linux/types.h>

#include <asm/ptrace.h>



static inline int syscall_get_arch(struct task_struct *task)

{
@@ -12,7 +16,91 @@ static inline int syscall_get_arch(struct task_struct *task) 
static inline long syscall_get_return_value(struct task_struct *task,

					    struct pt_regs *regs)

{

	return regs->r0;

	return regs->r19 ? -(long)regs->r0 : (long)regs->r0;

}



/*

 * Alpha syscall ABI / kernel conventions:

 *  - PAL provides syscall number in r0 on entry.

 *  - The kernel tracks the active syscall number in regs->r1 (mutable) and

 *    preserves the original syscall number in regs->r2 for rollback/restart.

 *  - Return value is in regs->r0, with regs->r19 ("a3") as the error flag

 *    (0=success, 1=error; on error regs->r0 holds positive errno).

 */



static inline long syscall_get_nr(struct task_struct *task,

				struct pt_regs *regs)

{

	return (long)regs->r1;

}



static inline void syscall_set_nr(struct task_struct *task,

				struct pt_regs *regs,

				long nr)

{

	regs->r1 = (unsigned long)nr;

}



/*

 * Syscall arguments:

 *   regs->r16..regs->r21 carry up to 6 syscall arguments on entry.

 *   Note: regs->r19 is also used as "a3" (error flag) on syscall return.

 */



static inline void syscall_get_arguments(struct task_struct *task,

					struct pt_regs *regs,

					unsigned long *args)

{

	args[0] = regs->r16;

	args[1] = regs->r17;

	args[2] = regs->r18;

	args[3] = regs->r19;

	args[4] = regs->r20;

	args[5] = regs->r21;

}



static inline void syscall_set_arguments(struct task_struct *task,

					struct pt_regs *regs,

					const unsigned long *args)

{

	regs->r16 = args[0];

	regs->r17 = args[1];

	regs->r18 = args[2];

	regs->r19 = args[3];

	regs->r20 = args[4];

	regs->r21 = args[5];

}

/*

 * Set return value for a syscall.

 * Alpha uses r0 for return value and r19 ("a3") as the error indicator:

 *   a3 = 0 => success

 *   a3 = 1 => error, and userspace interprets r0 as errno (positive).

 *

 * The kernel reports errors to userspace by setting a3=1 and placing a

 * positive errno value in r0. Some syscall paths do this in entry.S,

 * while others (e.g. seccomp/ptrace helpers) use syscall_set_return_value().

 */



static inline void syscall_set_return_value(struct task_struct *task,

					struct pt_regs *regs,

					int error, long val)

{



	if (error) {

		/* error is negative errno in this tree */

		regs->r0  = (unsigned long)(-error);  /* positive errno */

		regs->r19 = 1;                        /* a3 = error */

	} else {

		regs->r0  = (unsigned long)val;

		regs->r19 = 0;                        /* a3 = success */

	}

}



/* Restore the original syscall nr after seccomp/ptrace modified regs->r1. */

static inline void syscall_rollback(struct task_struct *task,

					struct pt_regs *regs)

{

	regs->r1 = regs->r2;

}



#endif	/* _ASM_ALPHA_SYSCALL_H */

arch/alpha/include/asm/thread_info.h

+15 −1
Original line number Diff line number Diff line
@@ -56,7 +56,8 @@ register unsigned long *current_stack_pointer __asm__ ("$30"); 
 * - pending work-to-be-done flags come first and must be assigned to be

 *   within bits 0 to 7 to fit in and immediate operand.

 *

 * TIF_SYSCALL_TRACE is known to be 0 via blbs.

 * (Historically TIF_SYSCALL_TRACE was known to be 0 via blbs, but we may

 *  also test multiple bits via masks now.)

 */

#define TIF_SYSCALL_TRACE	0	/* syscall trace active */

#define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
@@ -64,6 +65,7 @@ register unsigned long *current_stack_pointer __asm__ ("$30"); 
#define TIF_NEED_RESCHED	3	/* rescheduling necessary */

#define TIF_SYSCALL_AUDIT	4	/* syscall audit active */

#define TIF_NOTIFY_SIGNAL	5	/* signal notifications exist */

#define TIF_SECCOMP		6	/* seccomp syscall filtering active */

#define TIF_DIE_IF_KERNEL	9	/* dik recursion lock */

#define TIF_MEMDIE		13	/* is terminating due to OOM killer */

#define TIF_POLLING_NRFLAG	14	/* idle is polling for TIF_NEED_RESCHED */
@@ -74,8 +76,20 @@ register unsigned long *current_stack_pointer __asm__ ("$30"); 
#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

#define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)

#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)

#define _TIF_SECCOMP		(1<<TIF_SECCOMP)

#define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)



/*

 * Work to do on syscall entry (in entry.S).

 * If you want this to exactly mirror what entry.S checks, keep it aligned

 * with the mask used before branching to syscall_trace_enter().

 */

#ifdef CONFIG_AUDITSYSCALL

# define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP)

#else

# define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SECCOMP)

#endif



/* Work to do on interrupt/exception return.  */

#define _TIF_WORK_MASK		(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \

				 _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL)