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Author SHA1 Message Date
Stephan Schreiber 136f39ddc5 Wrong asm register contraints in the futex implementation 
The Linux Kernel contains some inline assembly source code which has
wrong asm register constraints in arch/ia64/include/asm/futex.h.

I observed this on Kernel 3.2.23 but it is also true on the most
recent Kernel 3.9-rc1.

File arch/ia64/include/asm/futex.h:

static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
			      u32 oldval, u32 newval)
{
	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
		return -EFAULT;

	{
		register unsigned long r8 __asm ("r8");
		unsigned long prev;
		__asm__ __volatile__(
			"	mf;;					\n"
			"	mov %0=r0				\n"
			"	mov ar.ccv=%4;;				\n"
			"[1:]	cmpxchg4.acq %1=[%2],%3,ar.ccv		\n"
			"	.xdata4 \"__ex_table\", 1b-., 2f-.	\n"
			"[2:]"
			: "=r" (r8), "=r" (prev)
			: "r" (uaddr), "r" (newval),
			  "rO" ((long) (unsigned) oldval)
			: "memory");
		*uval = prev;
		return r8;
	}
}

The list of output registers is
			: "=r" (r8), "=r" (prev)
The constraint "=r" means that the GCC has to maintain that these vars
are in registers and contain valid info when the program flow leaves
the assembly block (output registers).
But "=r" also means that GCC can put them in registers that are used
as input registers. Input registers are uaddr, newval, oldval on the
example.
The second assembly instruction
			"	mov %0=r0				\n"
is the first one which writes to a register; it sets %0 to 0. %0 means
the first register operand; it is r8 here. (The r0 is read-only and
always 0 on the Itanium; it can be used if an immediate zero value is
needed.)
This instruction might overwrite one of the other registers which are
still needed.
Whether it really happens depends on how GCC decides what registers it
uses and how it optimizes the code.

The objdump utility can give us disassembly.
The futex_atomic_cmpxchg_inatomic() function is inline, so we have to
look for a module that uses the funtion. This is the
cmpxchg_futex_value_locked() function in
kernel/futex.c:

static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
				      u32 uval, u32 newval)
{
	int ret;

	pagefault_disable();
	ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
	pagefault_enable();

	return ret;
}

Now the disassembly. At first from the Kernel package 3.2.23 which has
been compiled with GCC 4.4, remeber this Kernel seemed to work:
objdump -d linux-3.2.23/debian/build/build_ia64_none_mckinley/kernel/futex.o

0000000000000230 <cmpxchg_futex_value_locked>:
      230:	0b 18 80 1b 18 21 	[MMI]       adds r3=3168,r13;;
      236:	80 40 0d 00 42 00 	            adds r8=40,r3
      23c:	00 00 04 00       	            nop.i 0x0;;
      240:	0b 50 00 10 10 10 	[MMI]       ld4 r10=[r8];;
      246:	90 08 28 00 42 00 	            adds r9=1,r10
      24c:	00 00 04 00       	            nop.i 0x0;;
      250:	09 00 00 00 01 00 	[MMI]       nop.m 0x0
      256:	00 48 20 20 23 00 	            st4 [r8]=r9
      25c:	00 00 04 00       	            nop.i 0x0;;
      260:	08 10 80 06 00 21 	[MMI]       adds r2=32,r3
      266:	00 00 00 02 00 00 	            nop.m 0x0
      26c:	02 08 f1 52       	            extr.u r16=r33,0,61
      270:	05 40 88 00 08 e0 	[MLX]       addp4 r8=r34,r0
      276:	ff ff 0f 00 00 e0 	            movl r15=0xfffffffbfff;;
      27c:	f1 f7 ff 65
      280:	09 70 00 04 18 10 	[MMI]       ld8 r14=[r2]
      286:	00 00 00 02 00 c0 	            nop.m 0x0
      28c:	f0 80 1c d0       	            cmp.ltu p6,p7=r15,r16;;
      290:	08 40 fc 1d 09 3b 	[MMI]       cmp.eq p8,p9=-1,r14
      296:	00 00 00 02 00 40 	            nop.m 0x0
      29c:	e1 08 2d d0       	            cmp.ltu p10,p11=r14,r33
      2a0:	56 01 10 00 40 10 	[BBB] (p10) br.cond.spnt.few 2e0
<cmpxchg_futex_value_locked+0xb0>
      2a6:	02 08 00 80 21 03 	      (p08) br.cond.dpnt.few 2b0
<cmpxchg_futex_value_locked+0x80>
      2ac:	40 00 00 41       	      (p06) br.cond.spnt.few 2e0
<cmpxchg_futex_value_locked+0xb0>
      2b0:	0a 00 00 00 22 00 	[MMI]       mf;;
      2b6:	80 00 00 00 42 00 	            mov r8=r0
      2bc:	00 00 04 00       	            nop.i 0x0
      2c0:	0b 00 20 40 2a 04 	[MMI]       mov.m ar.ccv=r8;;
      2c6:	10 1a 85 22 20 00 	            cmpxchg4.acq r33=[r33],r35,ar.ccv
      2cc:	00 00 04 00       	            nop.i 0x0;;
      2d0:	10 00 84 40 90 11 	[MIB]       st4 [r32]=r33
      2d6:	00 00 00 02 00 00 	            nop.i 0x0
      2dc:	20 00 00 40       	            br.few 2f0
<cmpxchg_futex_value_locked+0xc0>
      2e0:	09 40 c8 f9 ff 27 	[MMI]       mov r8=-14
      2e6:	00 00 00 02 00 00 	            nop.m 0x0
      2ec:	00 00 04 00       	            nop.i 0x0;;
      2f0:	0b 58 20 1a 19 21 	[MMI]       adds r11=3208,r13;;
      2f6:	20 01 2c 20 20 00 	            ld4 r18=[r11]
      2fc:	00 00 04 00       	            nop.i 0x0;;
      300:	0b 88 fc 25 3f 23 	[MMI]       adds r17=-1,r18;;
      306:	00 88 2c 20 23 00 	            st4 [r11]=r17
      30c:	00 00 04 00       	            nop.i 0x0;;
      310:	11 00 00 00 01 00 	[MIB]       nop.m 0x0
      316:	00 00 00 02 00 80 	            nop.i 0x0
      31c:	08 00 84 00       	            br.ret.sptk.many b0;;

The lines
      2b0:	0a 00 00 00 22 00 	[MMI]       mf;;
      2b6:	80 00 00 00 42 00 	            mov r8=r0
      2bc:	00 00 04 00       	            nop.i 0x0
      2c0:	0b 00 20 40 2a 04 	[MMI]       mov.m ar.ccv=r8;;
      2c6:	10 1a 85 22 20 00 	            cmpxchg4.acq r33=[r33],r35,ar.ccv
      2cc:	00 00 04 00       	            nop.i 0x0;;
are the instructions of the assembly block.
The line
      2b6:	80 00 00 00 42 00 	            mov r8=r0
sets the r8 register to 0 and after that
      2c0:	0b 00 20 40 2a 04 	[MMI]       mov.m ar.ccv=r8;;
prepares the 'oldvalue' for the cmpxchg but it takes it from r8. This
is wrong.
What happened here is what I explained above: An input register is
overwritten which is still needed.
The register operand constraints in futex.h are wrong.

(The problem doesn't occur when the Kernel is compiled with GCC 4.6.)

The attached patch fixes the register operand constraints in futex.h.
The code after patching of it:

static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
			      u32 oldval, u32 newval)
{
	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
		return -EFAULT;

	{
		register unsigned long r8 __asm ("r8") = 0;
		unsigned long prev;
		__asm__ __volatile__(
			"	mf;;					\n"
			"	mov ar.ccv=%4;;				\n"
			"[1:]	cmpxchg4.acq %1=[%2],%3,ar.ccv		\n"
			"	.xdata4 \"__ex_table\", 1b-., 2f-.	\n"
			"[2:]"
			: "+r" (r8), "=&r" (prev)
			: "r" (uaddr), "r" (newval),
			  "rO" ((long) (unsigned) oldval)
			: "memory");
		*uval = prev;
		return r8;
	}
}

I also initialized the 'r8' var with the C programming language.
The _asm qualifier on the definition of the 'r8' var forces GCC to use
the r8 processor register for it.
I don't believe that we should use inline assembly for zeroing out a
local variable.
The constraint is
"+r" (r8)
what means that it is both an input register and an output register.
Note that the page fault handler will modify the r8 register which
will be the return value of the function.
The real fix is
"=&r" (prev)
The & means that GCC must not use any of the input registers to place
this output register in.

Patched the Kernel 3.2.23 and compiled it with GCC4.4:

0000000000000230 <cmpxchg_futex_value_locked>:
      230:	0b 18 80 1b 18 21 	[MMI]       adds r3=3168,r13;;
      236:	80 40 0d 00 42 00 	            adds r8=40,r3
      23c:	00 00 04 00       	            nop.i 0x0;;
      240:	0b 50 00 10 10 10 	[MMI]       ld4 r10=[r8];;
      246:	90 08 28 00 42 00 	            adds r9=1,r10
      24c:	00 00 04 00       	            nop.i 0x0;;
      250:	09 00 00 00 01 00 	[MMI]       nop.m 0x0
      256:	00 48 20 20 23 00 	            st4 [r8]=r9
      25c:	00 00 04 00       	            nop.i 0x0;;
      260:	08 10 80 06 00 21 	[MMI]       adds r2=32,r3
      266:	20 12 01 10 40 00 	            addp4 r34=r34,r0
      26c:	02 08 f1 52       	            extr.u r16=r33,0,61
      270:	05 40 00 00 00 e1 	[MLX]       mov r8=r0
      276:	ff ff 0f 00 00 e0 	            movl r15=0xfffffffbfff;;
      27c:	f1 f7 ff 65
      280:	09 70 00 04 18 10 	[MMI]       ld8 r14=[r2]
      286:	00 00 00 02 00 c0 	            nop.m 0x0
      28c:	f0 80 1c d0       	            cmp.ltu p6,p7=r15,r16;;
      290:	08 40 fc 1d 09 3b 	[MMI]       cmp.eq p8,p9=-1,r14
      296:	00 00 00 02 00 40 	            nop.m 0x0
      29c:	e1 08 2d d0       	            cmp.ltu p10,p11=r14,r33
      2a0:	56 01 10 00 40 10 	[BBB] (p10) br.cond.spnt.few 2e0
<cmpxchg_futex_value_locked+0xb0>
      2a6:	02 08 00 80 21 03 	      (p08) br.cond.dpnt.few 2b0
<cmpxchg_futex_value_locked+0x80>
      2ac:	40 00 00 41       	      (p06) br.cond.spnt.few 2e0
<cmpxchg_futex_value_locked+0xb0>
      2b0:	0b 00 00 00 22 00 	[MMI]       mf;;
      2b6:	00 10 81 54 08 00 	            mov.m ar.ccv=r34
      2bc:	00 00 04 00       	            nop.i 0x0;;
      2c0:	09 58 8c 42 11 10 	[MMI]       cmpxchg4.acq r11=[r33],r35,ar.ccv
      2c6:	00 00 00 02 00 00 	            nop.m 0x0
      2cc:	00 00 04 00       	            nop.i 0x0;;
      2d0:	10 00 2c 40 90 11 	[MIB]       st4 [r32]=r11
      2d6:	00 00 00 02 00 00 	            nop.i 0x0
      2dc:	20 00 00 40       	            br.few 2f0
<cmpxchg_futex_value_locked+0xc0>
      2e0:	09 40 c8 f9 ff 27 	[MMI]       mov r8=-14
      2e6:	00 00 00 02 00 00 	            nop.m 0x0
      2ec:	00 00 04 00       	            nop.i 0x0;;
      2f0:	0b 88 20 1a 19 21 	[MMI]       adds r17=3208,r13;;
      2f6:	30 01 44 20 20 00 	            ld4 r19=[r17]
      2fc:	00 00 04 00       	            nop.i 0x0;;
      300:	0b 90 fc 27 3f 23 	[MMI]       adds r18=-1,r19;;
      306:	00 90 44 20 23 00 	            st4 [r17]=r18
      30c:	00 00 04 00       	            nop.i 0x0;;
      310:	11 00 00 00 01 00 	[MIB]       nop.m 0x0
      316:	00 00 00 02 00 80 	            nop.i 0x0
      31c:	08 00 84 00       	            br.ret.sptk.many b0;;

Much better.
There is a
      270:	05 40 00 00 00 e1 	[MLX]       mov r8=r0
which was generated by C code r8 = 0. Below
      2b6:	00 10 81 54 08 00 	            mov.m ar.ccv=r34
what means that oldval is no longer overwritten.

This is Debian bug#702641
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=702641).

The patch is applicable on Kernel 3.9-rc1, 3.2.23 and many other versions.

Signed-off-by: Stephan Schreiber <info@fs-driver.org>
Cc: stable@vger.kernel.org
Signed-off-by: Tony Luck <tony.luck@intel.com>
 2013-03-19 16:14:53 -07:00
Luck, Tony c76f39bddb ia64: fix futex_atomic_cmpxchg_inatomic() 
Michel Lespinasse cleaned up the futex calling conventions in commit
37a9d912b2 ("futex: Sanitize cmpxchg_futex_value_locked API").

But the ia64 implementation was subtly broken.  Gcc does not know that
register "r8" will be updated by the fault handler if the cmpxchg
instruction takes an exception.  So it feels safe in letting the
initialization of r8 slide to after the cmpxchg.  Result: we always
return 0 whether the user address faulted or not.

Fix by moving the initialization of r8 into the __asm__ code so gcc
won't move it.

Reported-by: <emeric.maschino@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=42757
Tested-by: <emeric.maschino@gmail.com>
Acked-by: Michel Lespinasse <walken@google.com>
Cc: stable@vger.kernel.org # v2.6.39+
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2012-04-16 18:30:01 -07:00
David Howells c140d87995 Disintegrate asm/system.h for IA64 
Disintegrate asm/system.h for IA64.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Tony Luck <tony.luck@intel.com>
cc: linux-ia64@vger.kernel.org
 2012-03-28 18:30:02 +01:00
Michel Lespinasse 8d7718aa08 futex: Sanitize futex ops argument types 
Change futex_atomic_op_inuser and futex_atomic_cmpxchg_inatomic
prototypes to use u32 types for the futex as this is the data type the
futex core code uses all over the place.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311025058.GD26122@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
 2011-03-11 12:23:31 +01:00
Michel Lespinasse 37a9d912b2 futex: Sanitize cmpxchg_futex_value_locked API 
The cmpxchg_futex_value_locked API was funny in that it returned either
the original, user-exposed futex value OR an error code such as -EFAULT.
This was confusing at best, and could be a source of livelocks in places
that retry the cmpxchg_futex_value_locked after trying to fix the issue
by running fault_in_user_writeable().
    
This change makes the cmpxchg_futex_value_locked API more similar to the
get_futex_value_locked one, returning an error code and updating the
original value through a reference argument.
    
Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>  [tile]
Acked-by: Tony Luck <tony.luck@intel.com>  [ia64]
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Simek <monstr@monstr.eu>  [microblaze]
Acked-by: David Howells <dhowells@redhat.com> [frv]
Cc: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110311024851.GC26122@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
 2011-03-11 12:23:08 +01:00
Tony Luck 7f30491ccd [IA64] Move include/asm-ia64 to arch/ia64/include/asm 
After moving the the include files there were a few clean-ups:

1) Some files used #include <asm-ia64/xyz.h>, changed to <asm/xyz.h>

2) Some comments alerted maintainers to look at various header files to
make matching updates if certain code were to be changed. Updated these
comments to use the new include paths.

3) Some header files mentioned their own names in initial comments. Just
deleted these self references.

Signed-off-by: Tony Luck <tony.luck@intel.com>
 2008-08-01 10:21:21 -07:00