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Subject[PATCH v6 2/9] kernel: entry: Support TIF_SYSCAL_INTERCEPT on common entry code
Date
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)
+{
+ 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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