Date:   Fri, 29 Nov 2019 18:21:32 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        Pedro Alves <palves@...hat.com>, Peter Anvin <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix
 get_nr_restart_syscall()

On 11/28, Linus Torvalds wrote:
>
> > --- a/arch/x86/include/asm/signal.h
> > +++ b/arch/x86/include/asm/signal.h
> > @@ -5,6 +5,10 @@
> >  #ifndef __ASSEMBLY__
> >  #include <linux/linkage.h>
> >
> > +struct restart_block;
> > +extern void arch_set_restart_data(struct restart_block *);
> > +#define arch_set_restart_data  arch_set_restart_data
> 
> I'd just replace this with
> 
>    /* We need to save TS_COMPAT at the time of the call */
>    #define arch_set_restart_data(blk) (blk)->arch_data =
> current_thread_info()->status

OK, but then this code should live in {linux,asm}/thread_info.h. And this
is probably better, linux/thread_info.h already includes restart_block.h.

What do you think about 1-4 below?

Please note that 3/4 adds TS_COMPAT_RESTART you do not like, 4/4 kills it
and adds restart_block->arch_data.

This is because I will need to backport this fix, and 4/4 is not trivially
backportable due to KABI issues.

Oleg.


>From d1000d6f52ede3875c633067a5ec34e7ba138bc4 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@...hat.com>
Date: Fri, 29 Nov 2019 16:51:12 +0100
Subject: [PATCH 1/4] introduce set_restart_fn()

---
 fs/select.c                    | 10 ++++------
 include/linux/thread_info.h    | 12 ++++++++++++
 kernel/futex.c                 |  3 +--
 kernel/time/alarmtimer.c       |  2 +-
 kernel/time/hrtimer.c          |  2 +-
 kernel/time/posix-cpu-timers.c |  2 +-
 6 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 53a0c14..e517960 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -1037,10 +1037,9 @@ static long do_restart_poll(struct restart_block *restart_block)
 
 	ret = do_sys_poll(ufds, nfds, to);
 
-	if (ret == -ERESTARTNOHAND) {
-		restart_block->fn = do_restart_poll;
-		ret = -ERESTART_RESTARTBLOCK;
-	}
+	if (ret == -ERESTARTNOHAND)
+		ret = set_restart_fn(restart_block, do_restart_poll);
+
 	return ret;
 }
 
@@ -1062,7 +1061,6 @@ SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
 		struct restart_block *restart_block;
 
 		restart_block = &current->restart_block;
-		restart_block->fn = do_restart_poll;
 		restart_block->poll.ufds = ufds;
 		restart_block->poll.nfds = nfds;
 
@@ -1073,7 +1071,7 @@ SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
 		} else
 			restart_block->poll.has_timeout = 0;
 
-		ret = -ERESTART_RESTARTBLOCK;
+		ret = set_restart_fn(restart_block, do_restart_poll);
 	}
 	return ret;
 }
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 659a440..df8e3fb 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -39,6 +39,18 @@ enum {
 
 #ifdef __KERNEL__
 
+#ifndef arch_set_restart_data
+#define arch_set_restart_data(restart) do { } while (0)
+#endif
+
+static inline long set_restart_fn(struct restart_block *restart,
+					long (*fn)(struct restart_block *))
+{
+	restart->fn = fn;
+	arch_set_restart_data(restart);
+	return -ERESTART_RESTARTBLOCK;
+}
+
 #ifndef THREAD_ALIGN
 #define THREAD_ALIGN	THREAD_SIZE
 #endif
diff --git a/kernel/futex.c b/kernel/futex.c
index bd18f60..f4f20e9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2753,14 +2753,13 @@ static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 		goto out;
 
 	restart = &current->restart_block;
-	restart->fn = futex_wait_restart;
 	restart->futex.uaddr = uaddr;
 	restart->futex.val = val;
 	restart->futex.time = *abs_time;
 	restart->futex.bitset = bitset;
 	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
 
-	ret = -ERESTART_RESTARTBLOCK;
+	ret = set_restart_fn(restart, futex_wait_restart);
 
 out:
 	if (to) {
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 451f9d0..a2ddf56 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -829,9 +829,9 @@ static int alarm_timer_nsleep(const clockid_t which_clock, int flags,
 	if (flags == TIMER_ABSTIME)
 		return -ERESTARTNOHAND;
 
-	restart->fn = alarm_timer_nsleep_restart;
 	restart->nanosleep.clockid = type;
 	restart->nanosleep.expires = exp;
+	set_restart_fn(restart, alarm_timer_nsleep_restart);
 	return ret;
 }
 
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 6560553..55f71c4 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1932,9 +1932,9 @@ long hrtimer_nanosleep(const struct timespec64 *rqtp,
 	}
 
 	restart = &current->restart_block;
-	restart->fn = hrtimer_nanosleep_restart;
 	restart->nanosleep.clockid = t.timer.base->clockid;
 	restart->nanosleep.expires = hrtimer_get_expires_tv64(&t.timer);
+	set_restart_fn(restart, hrtimer_nanosleep_restart);
 out:
 	destroy_hrtimer_on_stack(&t.timer);
 	return ret;
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 42d512f..eacb0ca 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1335,8 +1335,8 @@ static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
 		if (flags & TIMER_ABSTIME)
 			return -ERESTARTNOHAND;
 
-		restart_block->fn = posix_cpu_nsleep_restart;
 		restart_block->nanosleep.clockid = which_clock;
+		set_restart_fn(restart_block, posix_cpu_nsleep_restart);
 	}
 	return error;
 }
-- 
2.5.0


>From 54301a07a645a27c982c99e4e975321cf73c5456 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@...hat.com>
Date: Fri, 29 Nov 2019 17:45:16 +0100
Subject: [PATCH 2/4] x86: mv TS_COMPAT from asm/processor.h to
 asm/thread_info.h

---
 arch/x86/include/asm/processor.h   | 9 ---------
 arch/x86/include/asm/thread_info.h | 9 +++++++++
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 54f5d54..d247a24 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -507,15 +507,6 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,
 }
 
 /*
- * Thread-synchronous status.
- *
- * This is different from the flags in that nobody else
- * ever touches our thread-synchronous status, so we don't
- * have to worry about atomic accesses.
- */
-#define TS_COMPAT		0x0002	/* 32bit syscall active (64BIT)*/
-
-/*
  * Set IOPL bits in EFLAGS from given mask
  */
 static inline void native_set_iopl_mask(unsigned mask)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f945353..b2125c4 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -221,6 +221,15 @@ static inline int arch_within_stack_frames(const void * const stack,
 
 #endif
 
+/*
+ * Thread-synchronous status.
+ *
+ * This is different from the flags in that nobody else
+ * ever touches our thread-synchronous status, so we don't
+ * have to worry about atomic accesses.
+ */
+#define TS_COMPAT		0x0002	/* 32bit syscall active (64BIT)*/
+
 #ifdef CONFIG_COMPAT
 #define TS_I386_REGS_POKED	0x0004	/* regs poked by 32-bit ptracer */
 #endif
-- 
2.5.0


>From db3784d4100cf3bc3097738da9a80fcfb6933fc6 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@...hat.com>
Date: Fri, 29 Nov 2019 17:52:42 +0100
Subject: [PATCH 3/4] ptrace/x86: introduce TS_COMPAT_RESTART to fix
 get_nr_restart_syscall()

---
 arch/x86/include/asm/thread_info.h | 14 +++++++++++++-
 arch/x86/kernel/signal.c           | 24 +-----------------------
 2 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index b2125c4..a4de7aa 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -230,10 +230,22 @@ static inline int arch_within_stack_frames(const void * const stack,
  */
 #define TS_COMPAT		0x0002	/* 32bit syscall active (64BIT)*/
 
+#ifndef __ASSEMBLY__
 #ifdef CONFIG_COMPAT
 #define TS_I386_REGS_POKED	0x0004	/* regs poked by 32-bit ptracer */
+#define TS_COMPAT_RESTART	0x0008
+
+#define arch_set_restart_data	arch_set_restart_data
+
+static inline void arch_set_restart_data(struct restart_block *restart)
+{
+	struct thread_info *ti = current_thread_info();
+	if (ti->status & TS_COMPAT)
+		ti->status |= TS_COMPAT_RESTART;
+	else
+		ti->status &= ~TS_COMPAT_RESTART;
+}
 #endif
-#ifndef __ASSEMBLY__
 
 #ifdef CONFIG_X86_32
 #define in_ia32_syscall() true
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 8eb7193..2fdbf5e 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -770,30 +770,8 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 
 static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
 {
-	/*
-	 * This function is fundamentally broken as currently
-	 * implemented.
-	 *
-	 * The idea is that we want to trigger a call to the
-	 * restart_block() syscall and that we want in_ia32_syscall(),
-	 * in_x32_syscall(), etc. to match whatever they were in the
-	 * syscall being restarted.  We assume that the syscall
-	 * instruction at (regs->ip - 2) matches whatever syscall
-	 * instruction we used to enter in the first place.
-	 *
-	 * The problem is that we can get here when ptrace pokes
-	 * syscall-like values into regs even if we're not in a syscall
-	 * at all.
-	 *
-	 * For now, we maintain historical behavior and guess based on
-	 * stored state.  We could do better by saving the actual
-	 * syscall arch in restart_block or (with caveats on x32) by
-	 * checking if regs->ip points to 'int $0x80'.  The current
-	 * behavior is incorrect if a tracer has a different bitness
-	 * than the tracee.
-	 */
 #ifdef CONFIG_IA32_EMULATION
-	if (current_thread_info()->status & (TS_COMPAT|TS_I386_REGS_POKED))
+	if (current_thread_info()->status & TS_COMPAT_RESTART)
 		return __NR_ia32_restart_syscall;
 #endif
 #ifdef CONFIG_X86_X32_ABI
-- 
2.5.0


>From f3b1ab409152d2c8ea9c75f7688b54aa6a3cf518 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@...hat.com>
Date: Fri, 29 Nov 2019 18:05:04 +0100
Subject: [PATCH 4/4] x86: turn TS_COMPAT_RESTART into restart_block->arch_data

---
 arch/x86/include/asm/thread_info.h | 12 ++----------
 arch/x86/kernel/signal.c           |  2 +-
 include/linux/restart_block.h      |  1 +
 3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index a4de7aa..75c4a0a 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -233,18 +233,10 @@ static inline int arch_within_stack_frames(const void * const stack,
 #ifndef __ASSEMBLY__
 #ifdef CONFIG_COMPAT
 #define TS_I386_REGS_POKED	0x0004	/* regs poked by 32-bit ptracer */
-#define TS_COMPAT_RESTART	0x0008
 
-#define arch_set_restart_data	arch_set_restart_data
+#define arch_set_restart_data(restart)	\
+	do { restart->arch_data = current_thread_info()->status; } while (0)
 
-static inline void arch_set_restart_data(struct restart_block *restart)
-{
-	struct thread_info *ti = current_thread_info();
-	if (ti->status & TS_COMPAT)
-		ti->status |= TS_COMPAT_RESTART;
-	else
-		ti->status &= ~TS_COMPAT_RESTART;
-}
 #endif
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 2fdbf5e..2e52767 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -771,7 +771,7 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
 {
 #ifdef CONFIG_IA32_EMULATION
-	if (current_thread_info()->status & TS_COMPAT_RESTART)
+	if (current->restart_block.arch_data & TS_COMPAT)
 		return __NR_ia32_restart_syscall;
 #endif
 #ifdef CONFIG_X86_X32_ABI
diff --git a/include/linux/restart_block.h b/include/linux/restart_block.h
index bba2920..980a655 100644
--- a/include/linux/restart_block.h
+++ b/include/linux/restart_block.h
@@ -23,6 +23,7 @@ enum timespec_type {
  * System call restart block.
  */
 struct restart_block {
+	unsigned long arch_data;
 	long (*fn)(struct restart_block *);
 	union {
 		/* For futex_wait and futex_wait_requeue_pi */
-- 
2.5.0

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