x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Mikulas Patocka]

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Hi

In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process 
is killed with SIGKILL after returning from any signal handler.

I use Debian sid x64-64 distribution with x32 architecture added from 
debian-ports.

I bisected the bug and found out that it is caused by the patch 
6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add 
SA_{X32,IA32}_ABI sa_flags").

example (strace of a process after receiving the SIGWINCH signal):

epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
write(4, "\0", 1)                       = 1
rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
+++ killed by SIGSEGV +++
Neopravniny poistup do pamiti (SIGSEGV)

Mikulas

Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Mikulas Patocka]

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On Wed, 19 Oct 2016, Mikulas Patocka wrote:

> Hi
> 
> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process 
> is killed with SIGKILL after returning from any signal handler.

I should have said they are killed with SIGSEGV, not SIGKILL.

> I use Debian sid x64-64 distribution with x32 architecture added from 
> debian-ports.
> 
> I bisected the bug and found out that it is caused by the patch 
> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add 
> SA_{X32,IA32}_ABI sa_flags").
> 
> example (strace of a process after receiving the SIGWINCH signal):
> 
> epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
> --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
> poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
> write(4, "\0", 1)                       = 1
> rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
> +++ killed by SIGSEGV +++
> Neopravniny poistup do pamiti (SIGSEGV)
> 
> Mikulas

BTW. when I take core dump of the killed x32 process, it shows:

ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              CORE (Core file)
  Machine:                           Intel 80386
				^^^^^^^^^^^^^^^^^^^

So, the kernel somehow thinks that it is i386 process, not x32 process. A 
core dump of a real x32 process shows "Class: ELF32, Machine: Advanced 
Micro Devices X86-64".

Mikulas

Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Dmitry Safonov]

2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@redhat.com>:
>
>
> On Wed, 19 Oct 2016, Mikulas Patocka wrote:
>
>> Hi
>>
>> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process
>> is killed with SIGKILL after returning from any signal handler.
>
> I should have said they are killed with SIGSEGV, not SIGKILL.
>
>> I use Debian sid x64-64 distribution with x32 architecture added from
>> debian-ports.
>>
>> I bisected the bug and found out that it is caused by the patch
>> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add
>> SA_{X32,IA32}_ABI sa_flags").
>>
>> example (strace of a process after receiving the SIGWINCH signal):
>>
>> epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
>> --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
>> poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
>> write(4, "\0", 1)                       = 1
>> rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
>> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
>> +++ killed by SIGSEGV +++
>> Neoprávnìný pøístup do pamìti (SIGSEGV)
>>
>> Mikulas
>
> BTW. when I take core dump of the killed x32 process, it shows:
>
> ELF Header:
>   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
>   Class:                             ELF32
>   Data:                              2's complement, little endian
>   Version:                           1 (current)
>   OS/ABI:                            UNIX - System V
>   ABI Version:                       0
>   Type:                              CORE (Core file)
>   Machine:                           Intel 80386
>                                 ^^^^^^^^^^^^^^^^^^^
>
> So, the kernel somehow thinks that it is i386 process, not x32 process. A
> core dump of a real x32 process shows "Class: ELF32, Machine: Advanced
> Micro Devices X86-64".

Thanks for catching, will check it today.

-- 
             Dmitry

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Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Dmitry Safonov]

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2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@redhat.com>:
>
>
> On Wed, 19 Oct 2016, Mikulas Patocka wrote:
>
>> Hi
>>
>> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process
>> is killed with SIGKILL after returning from any signal handler.
>
> I should have said they are killed with SIGSEGV, not SIGKILL.
>
>> I use Debian sid x64-64 distribution with x32 architecture added from
>> debian-ports.
>>
>> I bisected the bug and found out that it is caused by the patch
>> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add
>> SA_{X32,IA32}_ABI sa_flags").
>>
>> example (strace of a process after receiving the SIGWINCH signal):
>>
>> epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
>> --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
>> poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
>> write(4, "\0", 1)                       = 1
>> rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
>> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
>> +++ killed by SIGSEGV +++
>> Neoprávnìný pøístup do pamìti (SIGSEGV)
>>
>> Mikulas
>
> BTW. when I take core dump of the killed x32 process, it shows:
>
> ELF Header:
>   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
>   Class:                             ELF32
>   Data:                              2's complement, little endian
>   Version:                           1 (current)
>   OS/ABI:                            UNIX - System V
>   ABI Version:                       0
>   Type:                              CORE (Core file)
>   Machine:                           Intel 80386
>                                 ^^^^^^^^^^^^^^^^^^^
>
> So, the kernel somehow thinks that it is i386 process, not x32 process. A
> core dump of a real x32 process shows "Class: ELF32, Machine: Advanced
> Micro Devices X86-64".

Hi Mikulas,

could you give attached patch a shot?
In about 10 hours I'll be at work and will have debian-x32 install,
but for now, I can't test it.
Thanks again on catching that.

-- 
             Dmitry

[-- Attachment #2: 0001-x86-signal-set-SA_X32_ABI-flag-for-x32-programs.patch --]
[-- Type: text/x-patch, Size: 1139 bytes --]

From a546f8da1d12676fe79c746d859eb1e17aa4c331 Mon Sep 17 00:00:00 2001
From: Dmitry Safonov <0x7f454c46@gmail.com>
Date: Thu, 20 Oct 2016 00:53:08 +0300
Subject: [PATCH] x86/signal: set SA_X32_ABI flag for x32 programs

For x32 programs cs register is __USER_CS, so it returns here
unconditionally - remove this check completely here.

Fixes: commit 6846351052e6 ("x86/signal: Add SA_{X32,IA32}_ABI sa_flags")

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
---
 arch/x86/kernel/signal_compat.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 40df33753bae..ec1f756f9dc9 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -105,9 +105,6 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
 	/* Don't let flags to be set from userspace */
 	act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
 
-	if (user_64bit_mode(current_pt_regs()))
-		return;
-
 	if (in_ia32_syscall())
 		act->sa.sa_flags |= SA_IA32_ABI;
 	if (in_x32_syscall())
-- 
2.10.0

Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Adam Borowski]

On Thu, Oct 20, 2016 at 01:02:59AM +0300, Dmitry Safonov wrote:
> 2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@redhat.com>:
> > On Wed, 19 Oct 2016, Mikulas Patocka wrote:
> >> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process
> >> is killed with SIGKILL after returning from any signal handler.
> >
> > I should have said they are killed with SIGSEGV, not SIGKILL.
> >
> >> I use Debian sid x64-64 distribution with x32 architecture added from
> >> debian-ports.
> >>
> >> I bisected the bug and found out that it is caused by the patch
> >> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add
> >> SA_{X32,IA32}_ABI sa_flags").
> >
> > So, the kernel somehow thinks that it is i386 process, not x32 process. A
> > core dump of a real x32 process shows "Class: ELF32, Machine: Advanced
> > Micro Devices X86-64".
> 
> could you give attached patch a shot?
> In about 10 hours I'll be at work and will have debian-x32 install,
> but for now, I can't test it.
> Thanks again on catching that.
> 

> From a546f8da1d12676fe79c746d859eb1e17aa4c331 Mon Sep 17 00:00:00 2001
> From: Dmitry Safonov <0x7f454c46@gmail.com>
> Date: Thu, 20 Oct 2016 00:53:08 +0300
> Subject: [PATCH] x86/signal: set SA_X32_ABI flag for x32 programs
> 
> For x32 programs cs register is __USER_CS, so it returns here
> unconditionally - remove this check completely here.
> 
> Fixes: commit 6846351052e6 ("x86/signal: Add SA_{X32,IA32}_ABI sa_flags")
> 
> Reported-by: Mikulas Patocka <mpatocka@redhat.com>
> Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
> ---
>  arch/x86/kernel/signal_compat.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index 40df33753bae..ec1f756f9dc9 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -105,9 +105,6 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
>  	/* Don't let flags to be set from userspace */
>  	act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
>  
> -	if (user_64bit_mode(current_pt_regs()))
> -		return;
> -
>  	if (in_ia32_syscall())
>  		act->sa.sa_flags |= SA_IA32_ABI;
>  	if (in_x32_syscall())
> -- 
> 2.10.0

Works for me.  Tested on general operation, a few by-hand checks and several
random package builds.

It'd be nice to check glibc's testsuite as well as it had recent regressions
caused by kernel changes on x32 (like https://bugs.debian.org/841240) but as
gcc-6 in sid is broken right now (fails to build kernel, glibc:amd64, etc),
I didn't bother that much.

Tested-by: Adam Borowski <kilobyte@angband.pl>

-- 
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throw away the fruits (can dump them into a cake, etc), let the drink age
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Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Thomas Gleixner]

On Thu, 20 Oct 2016, Dmitry Safonov wrote:
> could you give attached patch a shot?

Can you please stop sending attached patches? It's a pain to look at them
and it makes it hard to reply inline.

I applied it and rewrote the changelog because the one liner you slapped
into it is more than useless. Ditto for the completely misleading subject
line. Please be more careful with that. 

Thanks,

	tglx

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Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Dmitry Safonov]

2016-10-20 12:24 GMT+03:00 Thomas Gleixner <tglx@linutronix.de>:
> On Thu, 20 Oct 2016, Dmitry Safonov wrote:
>> could you give attached patch a shot?
>
> Can you please stop sending attached patches? It's a pain to look at them
> and it makes it hard to reply inline.

Sure, I've planned to resend it after get tested-by or when I test
on x32 by myself. Sorry about attaching and changelog.

> I applied it and rewrote the changelog because the one liner you slapped
> into it is more than useless. Ditto for the completely misleading subject
> line. Please be more careful with that.

Thanks, Thomas!

-- 
             Dmitry

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Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa_flags"

[Mikulas Patocka]

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On Thu, 20 Oct 2016, Dmitry Safonov wrote:

> 2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@redhat.com>:
> >
> >
> > On Wed, 19 Oct 2016, Mikulas Patocka wrote:
> >
> >> Hi
> >>
> >> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process
> >> is killed with SIGKILL after returning from any signal handler.
> >
> > I should have said they are killed with SIGSEGV, not SIGKILL.
> >
> >> I use Debian sid x64-64 distribution with x32 architecture added from
> >> debian-ports.
> >>
> >> I bisected the bug and found out that it is caused by the patch
> >> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add
> >> SA_{X32,IA32}_ABI sa_flags").
> >>
> >> example (strace of a process after receiving the SIGWINCH signal):
> >>
> >> epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
> >> --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
> >> poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
> >> write(4, "\0", 1)                       = 1
> >> rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
> >> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
> >> +++ killed by SIGSEGV +++
> >> NeoprA!vnA!nA 1/2  pA,A-stup do pamA!ti (SIGSEGV)
> >>
> >> Mikulas
> >
> > BTW. when I take core dump of the killed x32 process, it shows:
> >
> > ELF Header:
> >   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
> >   Class:                             ELF32
> >   Data:                              2's complement, little endian
> >   Version:                           1 (current)
> >   OS/ABI:                            UNIX - System V
> >   ABI Version:                       0
> >   Type:                              CORE (Core file)
> >   Machine:                           Intel 80386
> >                                 ^^^^^^^^^^^^^^^^^^^
> >
> > So, the kernel somehow thinks that it is i386 process, not x32 process. A
> > core dump of a real x32 process shows "Class: ELF32, Machine: Advanced
> > Micro Devices X86-64".
> 
> Hi Mikulas,
> 
> could you give attached patch a shot?
> In about 10 hours I'll be at work and will have debian-x32 install,
> but for now, I can't test it.
> Thanks again on catching that.
> 
> -- 
>              Dmitry

Yes, it fixes the bug.

Mikulas