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SubjectRe: [PATCH v6 2/9] kernel: entry: Support TIF_SYSCAL_INTERCEPT on common entry code
On Fri, Sep 04, 2020 at 04:31:40PM -0400, Gabriel Krisman Bertazi wrote:
> Syscalls that use common entry code (x86 at the moment of this writing)
> need to have their defines updated inside this commit. This added a
> measureable overhead of 1ns to seccomp_benchmark selftests on a
> bare-metal AMD system.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> ---
> arch/x86/include/asm/thread_info.h | 4 ++--
> include/linux/entry-common.h | 6 +-----
> kernel/entry/common.c | 24 +++++++++++++++++++++---
> 3 files changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> index 267701ae3d86..cf723181e1f2 100644
> --- a/arch/x86/include/asm/thread_info.h
> +++ b/arch/x86/include/asm/thread_info.h
> @@ -82,7 +82,7 @@ struct thread_info {
> #define TIF_SSBD 5 /* Speculative store bypass disable */
> #define TIF_SYSCALL_EMU 6 /* syscall emulation active */
> #define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
> -#define TIF_SECCOMP 8 /* secure computing */
> +#define TIF_SYSCALL_INTERCEPT 8 /* Intercept system call */
> #define TIF_SPEC_IB 9 /* Indirect branch speculation mitigation */
> #define TIF_SPEC_FORCE_UPDATE 10 /* Force speculation MSR update in context switch */
> #define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
> @@ -112,7 +112,7 @@ struct thread_info {
> #define _TIF_SSBD (1 << TIF_SSBD)
> #define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
> #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
> -#define _TIF_SECCOMP (1 << TIF_SECCOMP)
> +#define _TIF_SYSCALL_INTERCEPT (1 << TIF_SYSCALL_INTERCEPT)
> #define _TIF_SPEC_IB (1 << TIF_SPEC_IB)
> #define _TIF_SPEC_FORCE_UPDATE (1 << TIF_SPEC_FORCE_UPDATE)
> #define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index efebbffcd5cc..72ce9ca860c6 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -21,10 +21,6 @@
> # define _TIF_SYSCALL_TRACEPOINT (0)
> #endif
>
> -#ifndef _TIF_SECCOMP
> -# define _TIF_SECCOMP (0)
> -#endif
> -
> #ifndef _TIF_SYSCALL_AUDIT
> # define _TIF_SYSCALL_AUDIT (0)
> #endif
> @@ -45,7 +41,7 @@
> #endif
>
> #define SYSCALL_ENTER_WORK \
> - (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \
> + (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SYSCALL_INTERCEPT | \
> _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_EMU | \
> ARCH_SYSCALL_ENTER_WORK)
>
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index fcae019158ca..44fd089d59da 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -4,6 +4,7 @@
> #include <linux/entry-common.h>
> #include <linux/livepatch.h>
> #include <linux/audit.h>
> +#include <linux/syscall_intercept.h>
>
> #define CREATE_TRACE_POINTS
> #include <trace/events/syscalls.h>
> @@ -41,6 +42,20 @@ static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
> }
> }
>
> +static inline long do_syscall_intercept(struct pt_regs *regs)

Hey Gabriel,

I think you can drop the pt_regs argument and just have this be

static inline do_syscall_intercept(void)

otherwise

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

> +{
> + int sysint_work = READ_ONCE(current->syscall_intercept);
> + int ret;
> +
> + if (sysint_work & SYSINT_SECCOMP) {
> + ret = __secure_computing(NULL);
> + if (ret == -1L)
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> static long syscall_trace_enter(struct pt_regs *regs, long syscall,
> unsigned long ti_work)
> {
> @@ -53,9 +68,12 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
> return -1L;
> }
>
> - /* Do seccomp after ptrace, to catch any tracer changes. */
> - if (ti_work & _TIF_SECCOMP) {
> - ret = __secure_computing(NULL);
> + /*
> + * Do syscall interception like seccomp after ptrace, to catch
> + * any tracer changes.
> + */
> + if (ti_work & _TIF_SYSCALL_INTERCEPT) {
> + ret = do_syscall_intercept(regs);
> if (ret == -1L)
> return ret;
> }
> --
> 2.28.0

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