[tip: x86/entry] x86/entry: Use generic syscall exit functionality

From: tip-bot2 for Thomas Gleixner
Date: Fri Jul 24 2020 - 16:12:07 EST

The following commit has been merged into the x86/entry branch of tip:

Commit-ID: 167fd210ec0555d371a20435dac7c2c7052df7ed
Gitweb: https://git.kernel.org/tip/167fd210ec0555d371a20435dac7c2c7052df7ed
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 23 Jul 2020 00:00:05 +02:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 24 Jul 2020 15:04:59 +02:00

x86/entry: Use generic syscall exit functionality

Replace the x86 variant with the generic version. Provide the relevant
architecture specific helper functions and defines.

Use a temporary define for idtentry_exit_user which will be cleaned up
seperately.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200722220520.494648601@xxxxxxxxxxxxx


---
arch/x86/entry/common.c | 221 +---------------------------
arch/x86/entry/entry_32.S | 2 +-
arch/x86/entry/entry_64.S | 2 +-
arch/x86/include/asm/entry-common.h | 44 +++++-
arch/x86/include/asm/idtentry.h | 3 +-
arch/x86/include/asm/signal.h | 1 +-
arch/x86/kernel/signal.c | 3 +-
7 files changed, 54 insertions(+), 222 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index d2fe85f..bc96eb8 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -15,15 +15,8 @@
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
-#include <linux/tracehook.h>
-#include <linux/audit.h>
-#include <linux/signal.h>
#include <linux/export.h>
-#include <linux/context_tracking.h>
-#include <linux/user-return-notifier.h>
#include <linux/nospec.h>
-#include <linux/uprobes.h>
-#include <linux/livepatch.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>

@@ -42,191 +35,6 @@
#include <asm/syscall.h>
#include <asm/irq_stack.h>

-#include <trace/events/syscalls.h>
-
-/**
- * exit_to_user_mode - Fixup state when exiting to user mode
- *
- * Syscall exit enables interrupts, but the kernel state is interrupts
- * disabled when this is invoked. Also tell RCU about it.
- *
- * 1) Trace interrupts on state
- * 2) Invoke context tracking if enabled to adjust RCU state
- * 3) Clear CPU buffers if CPU is affected by MDS and the migitation is on.
- * 4) Tell lockdep that interrupts are enabled
- */
-static __always_inline void exit_to_user_mode(void)
-{
- instrumentation_begin();
- trace_hardirqs_on_prepare();
- lockdep_hardirqs_on_prepare(CALLER_ADDR0);
- instrumentation_end();
-
- user_enter_irqoff();
- mds_user_clear_cpu_buffers();
- lockdep_hardirqs_on(CALLER_ADDR0);
-}
-
-#define EXIT_TO_USERMODE_LOOP_FLAGS \
- (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
- _TIF_NEED_RESCHED | _TIF_PATCH_PENDING)
-
-static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
-{
- /*
- * In order to return to user mode, we need to have IRQs off with
- * none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags
- * can be set at any time on preemptible kernels if we have IRQs on,
- * so we need to loop. Disabling preemption wouldn't help: doing the
- * work to clear some of the flags can sleep.
- */
- while (true) {
- /* We have work to do. */
- local_irq_enable();
-
- if (cached_flags & _TIF_NEED_RESCHED)
- schedule();
-
- if (cached_flags & _TIF_UPROBE)
- uprobe_notify_resume(regs);
-
- if (cached_flags & _TIF_PATCH_PENDING)
- klp_update_patch_state(current);
-
- /* deal with pending signal delivery */
- if (cached_flags & _TIF_SIGPENDING)
- do_signal(regs);
-
- if (cached_flags & _TIF_NOTIFY_RESUME) {
- clear_thread_flag(TIF_NOTIFY_RESUME);
- tracehook_notify_resume(regs);
- rseq_handle_notify_resume(NULL, regs);
- }
-
- /* Disable IRQs and retry */
- local_irq_disable();
-
- cached_flags = READ_ONCE(current_thread_info()->flags);
-
- if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
- break;
- }
-}
-
-static void __prepare_exit_to_usermode(struct pt_regs *regs)
-{
- struct thread_info *ti = current_thread_info();
- u32 cached_flags;
-
- addr_limit_user_check();
-
- lockdep_assert_irqs_disabled();
- lockdep_sys_exit();
-
- cached_flags = READ_ONCE(ti->flags);
-
- if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
- exit_to_usermode_loop(regs, cached_flags);
-
- /* Reload ti->flags; we may have rescheduled above. */
- cached_flags = READ_ONCE(ti->flags);
-
- if (cached_flags & _TIF_USER_RETURN_NOTIFY)
- fire_user_return_notifiers();
-
- if (unlikely(cached_flags & _TIF_IO_BITMAP))
- tss_update_io_bitmap();
-
- fpregs_assert_state_consistent();
- if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
- switch_fpu_return();
-
-#ifdef CONFIG_COMPAT
- /*
- * Compat syscalls set TS_COMPAT. Make sure we clear it before
- * returning to user mode. We need to clear it *after* signal
- * handling, because syscall restart has a fixup for compat
- * syscalls. The fixup is exercised by the ptrace_syscall_32
- * selftest.
- *
- * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
- * special case only applies after poking regs and before the
- * very next return to user mode.
- */
- ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
-#endif
-}
-
-static noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
-{
- instrumentation_begin();
- __prepare_exit_to_usermode(regs);
- instrumentation_end();
- exit_to_user_mode();
-}
-
-#define SYSCALL_EXIT_WORK_FLAGS \
- (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
- _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
-
-static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
-{
- bool step;
-
- audit_syscall_exit(regs);
-
- if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
- trace_sys_exit(regs, regs->ax);
-
- /*
- * If TIF_SYSCALL_EMU is set, we only get here because of
- * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
- * We already reported this syscall instruction in
- * syscall_trace_enter().
- */
- step = unlikely(
- (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
- == _TIF_SINGLESTEP);
- if (step || cached_flags & _TIF_SYSCALL_TRACE)
- tracehook_report_syscall_exit(regs, step);
-}
-
-static void __syscall_return_slowpath(struct pt_regs *regs)
-{
- struct thread_info *ti = current_thread_info();
- u32 cached_flags = READ_ONCE(ti->flags);
-
- CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
-
- if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
- WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
- local_irq_enable();
-
- rseq_syscall(regs);
-
- /*
- * First do one-time work. If these work items are enabled, we
- * want to run them exactly once per syscall exit with IRQs on.
- */
- if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
- syscall_slow_exit_work(regs, cached_flags);
-
- local_irq_disable();
- __prepare_exit_to_usermode(regs);
-}
-
-/*
- * Called with IRQs on and fully valid regs. Returns with IRQs off in a
- * state such that we can immediately switch to user mode.
- */
-__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
-{
- instrumentation_begin();
- __syscall_return_slowpath(regs);
- instrumentation_end();
- exit_to_user_mode();
-}
-
#ifdef CONFIG_X86_64
__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
{
@@ -245,7 +53,7 @@ __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
#endif
}
instrumentation_end();
- syscall_return_slowpath(regs);
+ syscall_exit_to_user_mode(regs);
}
#endif

@@ -284,7 +92,7 @@ __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
unsigned int nr = syscall_32_enter(regs);

do_syscall_32_irqs_on(regs, nr);
- syscall_return_slowpath(regs);
+ syscall_exit_to_user_mode(regs);
}

static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
@@ -310,13 +118,13 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
if (res) {
/* User code screwed up. */
regs->ax = -EFAULT;
- syscall_return_slowpath(regs);
+ syscall_exit_to_user_mode(regs);
return false;
}

/* Now this is just like a normal syscall. */
do_syscall_32_irqs_on(regs, nr);
- syscall_return_slowpath(regs);
+ syscall_exit_to_user_mode(regs);
return true;
}

@@ -524,7 +332,7 @@ void noinstr idtentry_exit(struct pt_regs *regs, idtentry_state_t state)

/* Check whether this returns to user mode */
if (user_mode(regs)) {
- prepare_exit_to_usermode(regs);
+ irqentry_exit_to_user_mode(regs);
} else if (regs->flags & X86_EFLAGS_IF) {
/*
* If RCU was not watching on entry this needs to be done
@@ -555,25 +363,6 @@ void noinstr idtentry_exit(struct pt_regs *regs, idtentry_state_t state)
}
}

-/**
- * idtentry_exit_user - Handle return from exception to user mode
- * @regs: Pointer to pt_regs (exception entry regs)
- *
- * Runs the necessary preemption and work checks and returns to the caller
- * with interrupts disabled and no further work pending.
- *
- * This is the last action before returning to the low level ASM code which
- * just needs to return to the appropriate context.
- *
- * Counterpart to idtentry_enter_user().
- */
-void noinstr idtentry_exit_user(struct pt_regs *regs)
-{
- lockdep_assert_irqs_disabled();
-
- prepare_exit_to_usermode(regs);
-}
-
#ifdef CONFIG_XEN_PV
#ifndef CONFIG_PREEMPTION
/*
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 2d0bd5d..6addbd1 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -846,7 +846,7 @@ SYM_CODE_START(ret_from_fork)
2:
/* When we fork, we trace the syscall return in the child, too. */
movl %esp, %eax
- call syscall_return_slowpath
+ call syscall_exit_to_user_mode
jmp .Lsyscall_32_done

/* kernel thread */
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d2a00c9..f423ca9 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -283,7 +283,7 @@ SYM_CODE_START(ret_from_fork)
2:
UNWIND_HINT_REGS
movq %rsp, %rdi
- call syscall_return_slowpath /* returns with IRQs disabled */
+ call syscall_exit_to_user_mode /* returns with IRQs disabled */
jmp swapgs_restore_regs_and_return_to_usermode

1:
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 7070b90..a8f9315 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -2,6 +2,12 @@
#ifndef _ASM_X86_ENTRY_COMMON_H
#define _ASM_X86_ENTRY_COMMON_H

+#include <linux/user-return-notifier.h>
+
+#include <asm/nospec-branch.h>
+#include <asm/io_bitmap.h>
+#include <asm/fpu/api.h>
+
/* Check that the stack and regs on entry from user mode are sane. */
static __always_inline void arch_check_user_regs(struct pt_regs *regs)
{
@@ -29,4 +35,42 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs)
}
#define arch_check_user_regs arch_check_user_regs

+#define ARCH_SYSCALL_EXIT_WORK (_TIF_SINGLESTEP)
+
+static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
+ unsigned long ti_work)
+{
+ if (ti_work & _TIF_USER_RETURN_NOTIFY)
+ fire_user_return_notifiers();
+
+ if (unlikely(ti_work & _TIF_IO_BITMAP))
+ tss_update_io_bitmap();
+
+ fpregs_assert_state_consistent();
+ if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
+ switch_fpu_return();
+
+#ifdef CONFIG_COMPAT
+ /*
+ * Compat syscalls set TS_COMPAT. Make sure we clear it before
+ * returning to user mode. We need to clear it *after* signal
+ * handling, because syscall restart has a fixup for compat
+ * syscalls. The fixup is exercised by the ptrace_syscall_32
+ * selftest.
+ *
+ * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
+ * special case only applies after poking regs and before the
+ * very next return to user mode.
+ */
+ current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
+#endif
+}
+#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
+
+static __always_inline void arch_exit_to_user_mode(void)
+{
+ mds_user_clear_cpu_buffers();
+}
+#define arch_exit_to_user_mode arch_exit_to_user_mode
+
#endif
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 449910f..f7d48ea 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -13,8 +13,7 @@

/* Temporary define */
#define idtentry_enter_user irqentry_enter_from_user_mode
-
-void idtentry_exit_user(struct pt_regs *regs);
+#define idtentry_exit_user irqentry_exit_to_user_mode

typedef struct idtentry_state {
bool exit_rcu;
diff --git a/arch/x86/include/asm/signal.h b/arch/x86/include/asm/signal.h
index 33d3c88..6fd8410 100644
--- a/arch/x86/include/asm/signal.h
+++ b/arch/x86/include/asm/signal.h
@@ -35,7 +35,6 @@ typedef sigset_t compat_sigset_t;
#endif /* __ASSEMBLY__ */
#include <uapi/asm/signal.h>
#ifndef __ASSEMBLY__
-extern void do_signal(struct pt_regs *regs);

#define __ARCH_HAS_SA_RESTORER

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 399f97a..d5fa494 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -25,6 +25,7 @@
#include <linux/user-return-notifier.h>
#include <linux/uprobes.h>
#include <linux/context_tracking.h>
+#include <linux/entry-common.h>
#include <linux/syscalls.h>

#include <asm/processor.h>
@@ -803,7 +804,7 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*/
-void do_signal(struct pt_regs *regs)
+void arch_do_signal(struct pt_regs *regs)
{
struct ksignal ksig;