BACKPORT: x86/entry: Get rid of two-phase syscall entry work

I added two-phase syscall entry work back when the entry slow path
was very slow.  Nowadays, the entry slow path is fast and two-phase
entry work serves no purpose.  Remove it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
(cherry picked from commit c87a85177e7a7f9a9ee32893fb99a928e02fe23a)

Bug: 119769499
Change-Id: Ieac4470411f88ca8830794d0322d8d8bb348039e
[ghackmann@google.com:
 - adjust for post-4.4 is_ia32_task() -> in_ia32_syscall() renaming
 - preserve TF flags fixup in syscall_trace_enter()
 - keep syscall_trace_enter() exported, since we haven't taken
   patches to move the calling code from entry_64.S to common.c]
Signed-off-by: Greg Hackmann <ghackmann@google.com>

2 files changed, 18 insertions, 90 deletions

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index a9e501303e15..05613b8da509 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -64,20 +64,13 @@ static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
 }
 
 /*
- * We can return 0 to resume the syscall or anything else to go to phase
- * 2.  If we resume the syscall, we need to put something appropriate in
- * regs->orig_ax.
- *
- * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
- * are fully functional.
- *
- * For phase 2's benefit, our return value is:
- * 0:			resume the syscall
- * 1:			go to phase 2; no seccomp phase 2 needed
- * anything else:	go to phase 2; pass return value to seccomp
+ * Returns the syscall nr to run (which should match regs->orig_ax) or -1
+ * to skip the syscall.
  */
-unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
+long syscall_trace_enter(struct pt_regs *regs)
 {
+	u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
+
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	unsigned long ret = 0;
 	u32 work;
@@ -98,6 +91,16 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 	}
 #endif
 
+	/*
+	 * If we stepped into a sysenter/syscall insn, it trapped in
+	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
+	 * If user-mode had set TF itself, then it's still clear from
+	 * do_debug() and we need to set it again to restore the user
+	 * state.  If we entered on the slow path, TF was already set.
+	 */
+	if (work & _TIF_SINGLESTEP)
+		regs->flags |= X86_EFLAGS_TF;
+
 #ifdef CONFIG_SECCOMP
 	/*
 	 * Do seccomp first -- it should minimize exposure of other
@@ -129,69 +132,9 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 			sd.args[5] = regs->bp;
 		}
 
-		BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
-		BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);
-
-		ret = seccomp_phase1(&sd);
-		if (ret == SECCOMP_PHASE1_SKIP) {
-			regs->orig_ax = -1;
-			ret = 0;
-		} else if (ret != SECCOMP_PHASE1_OK) {
-			return ret;  /* Go directly to phase 2 */
-		}
-
-		work &= ~_TIF_SECCOMP;
-	}
-#endif
-
-	/* Do our best to finish without phase 2. */
-	if (work == 0)
-		return ret;  /* seccomp and/or nohz only (ret == 0 here) */
-
-#ifdef CONFIG_AUDITSYSCALL
-	if (work == _TIF_SYSCALL_AUDIT) {
-		/*
-		 * If there is no more work to be done except auditing,
-		 * then audit in phase 1.  Phase 2 always audits, so, if
-		 * we audit here, then we can't go on to phase 2.
-		 */
-		do_audit_syscall_entry(regs, arch);
-		return 0;
-	}
-#endif
-
-	return 1;  /* Something is enabled that we can't handle in phase 1 */
-}
-
-/* Returns the syscall nr to run (which should match regs->orig_ax). */
-long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
-				unsigned long phase1_result)
-{
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
-	long ret = 0;
-	u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
-
-	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
-		BUG_ON(regs != task_pt_regs(current));
-
-	/*
-	 * If we stepped into a sysenter/syscall insn, it trapped in
-	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
-	 * If user-mode had set TF itself, then it's still clear from
-	 * do_debug() and we need to set it again to restore the user
-	 * state.  If we entered on the slow path, TF was already set.
-	 */
-	if (work & _TIF_SINGLESTEP)
-		regs->flags |= X86_EFLAGS_TF;
-
-#ifdef CONFIG_SECCOMP
-	/*
-	 * Call seccomp_phase2 before running the other hooks so that
-	 * they can see any changes made by a seccomp tracer.
-	 */
-	if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
-		/* seccomp failures shouldn't expose any additional code. */
-		return -1;
+		ret = __secure_computing(&sd);
+		if (ret == -1)
+			return ret;
 	}
 #endif
 
@@ -210,17 +153,6 @@ long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
 	return ret ?: regs->orig_ax;
 }
 
-long syscall_trace_enter(struct pt_regs *regs)
-{
-	u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
-	unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);
-
-	if (phase1_result == 0)
-		return regs->orig_ax;
-	else
-		return syscall_trace_enter_phase2(regs, arch, phase1_result);
-}
-
 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
 	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 6271281f947d..25479a144894 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -83,10 +83,6 @@ extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
 			 int error_code, int si_code);
 
 
-extern unsigned long syscall_trace_enter_phase1(struct pt_regs *, u32 arch);
-extern long syscall_trace_enter_phase2(struct pt_regs *, u32 arch,
-				       unsigned long phase1_result);
-
 extern long syscall_trace_enter(struct pt_regs *);
 
 static inline unsigned long regs_return_value(struct pt_regs *regs)