[PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Matus Kysel]

Used same style to handle another glibc reserved signal SIGSETXID (33), 
that is used by glibc NPTL setuid/setgid functions. This should fix problems
with application using those functions and failing with error
"qemu:handle_cpu_signal received signal outside vCPU context".

Signed-off-by: Matus Kysel <mkysel@tachyum.com>
---
 linux-user/signal.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 0128bde4d2..c59221fd0a 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
     [SIGPWR] = TARGET_SIGPWR,
     [SIGSYS] = TARGET_SIGSYS,
     /* next signals stay the same */
-    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
-       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-/
-       To fix this properly we need to do manual signal delivery multiplexed
-       over a single host signal.  */
+    /*
+     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and SIGRTMAX - 1
+     * to avoid overlap with host libpthread (NPTL glibc) signals.
+     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
+     * To fix this properly we need to do manual signal delivery multiplexed
+     * over a single host signal.
+     */
     [__SIGRTMIN] = __SIGRTMAX,
+    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
+    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
     [__SIGRTMAX] = __SIGRTMIN,
 };
 static uint8_t target_to_host_signal_table[_NSIG];
-- 
2.17.1

RE: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Matus Kysel]

Hi all,

It seems my patch was ignore. Ping!
 
https://patchew.org/QEMU/20200116115700.127951-1-mkysel@tachyum.com/

-----Original Message-----
From: Matus Kysel <mkysel@tachyum.com> 
Sent: štvrtok 16. januára 2020 12:57
Cc: Matus Kysel <mkysel@tachyum.com>; Riku Voipio <riku.voipio@iki.fi>; Laurent Vivier <laurent@vivier.eu>; open list:All patches CC here <qemu-devel@nongnu.org>
Subject: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

Used same style to handle another glibc reserved signal SIGSETXID (33), that is used by glibc NPTL setuid/setgid functions. This should fix problems with application using those functions and failing with error "qemu:handle_cpu_signal received signal outside vCPU context".

Signed-off-by: Matus Kysel <mkysel@tachyum.com>
---
 linux-user/signal.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c index 0128bde4d2..c59221fd0a 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
     [SIGPWR] = TARGET_SIGPWR,
     [SIGSYS] = TARGET_SIGSYS,
     /* next signals stay the same */
-    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
-       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-/
-       To fix this properly we need to do manual signal delivery multiplexed
-       over a single host signal.  */
+    /*
+     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and SIGRTMAX - 1
+     * to avoid overlap with host libpthread (NPTL glibc) signals.
+     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
+     * To fix this properly we need to do manual signal delivery multiplexed
+     * over a single host signal.
+     */
     [__SIGRTMIN] = __SIGRTMAX,
+    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
+    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
     [__SIGRTMAX] = __SIGRTMIN,
 };
 static uint8_t target_to_host_signal_table[_NSIG];
--
2.17.1

Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Peter Maydell]

On Thu, 16 Jan 2020 at 11:58, Matus Kysel <mkysel@tachyum.com> wrote:
>
> Used same style to handle another glibc reserved signal SIGSETXID (33),
> that is used by glibc NPTL setuid/setgid functions. This should fix problems
> with application using those functions and failing with error
> "qemu:handle_cpu_signal received signal outside vCPU context".
>
> Signed-off-by: Matus Kysel <mkysel@tachyum.com>
> ---
>  linux-user/signal.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 0128bde4d2..c59221fd0a 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>      [SIGPWR] = TARGET_SIGPWR,
>      [SIGSYS] = TARGET_SIGSYS,
>      /* next signals stay the same */
> -    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
> -       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-/
> -       To fix this properly we need to do manual signal delivery multiplexed
> -       over a single host signal.  */
> +    /*
> +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and SIGRTMAX - 1
> +     * to avoid overlap with host libpthread (NPTL glibc) signals.
> +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
> +     * To fix this properly we need to do manual signal delivery multiplexed
> +     * over a single host signal.
> +     */
>      [__SIGRTMIN] = __SIGRTMAX,
> +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
> +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
>      [__SIGRTMAX] = __SIGRTMIN,
>  };
>  static uint8_t target_to_host_signal_table[_NSIG];
> --
> 2.17.1

This is a long-standing known problem, but doing this is likely
to break currently-working guest binaries (notably things written
in Go). See for example the discussion on this thread:
https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html

thanks
-- PMM

RE: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Taylor Simpson]

I proposed a similar patch guarded by #ifdef TARGET_HEXAGON.  I understand we don't want to break things that are working, and we don't want to open the door for a bunch of #ifdef's here.  However, more than one scenario needs this capability.

Would a suitable compromise be to provide a hook in linux-user/signal.c for the target to put in the changes they need?

diff --git a/linux-user/hexagon/target_signal.h b/linux-user/hexagon/target_signal.h
index ae52ff5..f82f8c1 100644
--- a/linux-user/hexagon/target_signal.h
+++ b/linux-user/hexagon/target_signal.h
@@ -31,4 +31,15 @@ typedef struct target_sigaltstack {

 #include "../generic/signal.h"

+    /*
+     * Hexagon uses the same signal for pthread cancel as the host pthreads,
+     * so cannot be overridden.
+     * Therefore, we map Hexagon signal to a different host signal.
+     */
+#define SIGNAL_MODS \
+    [__SIGRTMIN + 1] = __SIGRTMAX - 1, \
+    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
+
+
+
 #endif /* TARGET_SIGNAL_H */
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 5ca6d62..ebca770 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -24,6 +24,7 @@
 #include "qemu.h"
 #include "trace.h"
 #include "signal-common.h"
+#include "target_signal.h"

 static struct target_sigaction sigact_table[TARGET_NSIG];

@@ -72,6 +73,9 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
        over a single host signal.  */
     [__SIGRTMIN] = __SIGRTMAX,
     [__SIGRTMAX] = __SIGRTMIN,
+#ifdef SIGNAL_MODS
+    SIGNAL_MODS
+#endif
 };
 static uint8_t target_to_host_signal_table[_NSIG];


Taylor


> -----Original Message-----
> From: Qemu-devel <qemu-devel-
> bounces+tsimpson=quicinc.com@nongnu.org> On Behalf Of Peter Maydell
> Sent: Tuesday, January 28, 2020 3:27 AM
> To: Matus Kysel <mkysel@tachyum.com>
> Cc: Riku Voipio <riku.voipio@iki.fi>; open list:All patches CC here <qemu-
> devel@nongnu.org>; Laurent Vivier <laurent@vivier.eu>
> Subject: Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid
>
> -------------------------------------------------------------------------
> CAUTION: This email originated from outside of the organization.
> -------------------------------------------------------------------------
>
> On Thu, 16 Jan 2020 at 11:58, Matus Kysel <mkysel@tachyum.com> wrote:
> >
> > Used same style to handle another glibc reserved signal SIGSETXID
> > (33), that is used by glibc NPTL setuid/setgid functions. This should
> > fix problems with application using those functions and failing with
> > error "qemu:handle_cpu_signal received signal outside vCPU context".
> >
> > Signed-off-by: Matus Kysel <mkysel@tachyum.com>
> > ---
> >  linux-user/signal.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/linux-user/signal.c b/linux-user/signal.c index
> > 0128bde4d2..c59221fd0a 100644
> > --- a/linux-user/signal.c
> > +++ b/linux-user/signal.c
> > @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] =
> {
> >      [SIGPWR] = TARGET_SIGPWR,
> >      [SIGSYS] = TARGET_SIGSYS,
> >      /* next signals stay the same */
> > -    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
> > -       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-
> /
> > -       To fix this properly we need to do manual signal delivery multiplexed
> > -       over a single host signal.  */
> > +    /*
> > +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and
> SIGRTMAX - 1
> > +     * to avoid overlap with host libpthread (NPTL glibc) signals.
> > +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
> > +     * To fix this properly we need to do manual signal delivery multiplexed
> > +     * over a single host signal.
> > +     */
> >      [__SIGRTMIN] = __SIGRTMAX,
> > +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
> > +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
> >      [__SIGRTMAX] = __SIGRTMIN,
> >  };
> >  static uint8_t target_to_host_signal_table[_NSIG];
> > --
> > 2.17.1
>
> This is a long-standing known problem, but doing this is likely to break
> currently-working guest binaries (notably things written in Go). See for
> example the discussion on this thread:
> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html
>
> thanks
> -- PMM

Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Peter Maydell]

On Tue, 28 Jan 2020 at 12:33, Taylor Simpson <tsimpson@quicinc.com> wrote:
>
> I proposed a similar patch guarded by #ifdef TARGET_HEXAGON.  I understand we don't want to break things that are working, and we don't want to open the door for a bunch of #ifdef's here.  However, more than one scenario needs this capability.
>
> Would a suitable compromise be to provide a hook in linux-user/signal.c for the target to put in the changes they need?

No; this isn't target-specific, and we don't want
per-target different behaviour.

thanks
-- PMM

Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Laurent Vivier]

Le 28/01/2020 à 13:45, Peter Maydell a écrit :
> On Tue, 28 Jan 2020 at 12:33, Taylor Simpson <tsimpson@quicinc.com> wrote:
>>
>> I proposed a similar patch guarded by #ifdef TARGET_HEXAGON.  I understand we don't want to break things that are working, and we don't want to open the door for a bunch of #ifdef's here.  However, more than one scenario needs this capability.
>>
>> Would a suitable compromise be to provide a hook in linux-user/signal.c for the target to put in the changes they need?
> 
> No; this isn't target-specific, and we don't want
> per-target different behaviour.

So I guess the only way to fix the problem is to implement the signal
multiplexing initiated by Milos [1] and tried again by Josh [2].

Any volunteer?

If not, I will try to find some time to do that...

Thanks,
Laurent

[1] "[PATCH 0/5] linux-user: Support signal passing for targets having
more signals than host"

https://patchew.org/QEMU/1558550785-20098-1-git-send-email-aleksandar.markovic@rt-rk.com/

[2] https://lists.gnu.org/archive/html/qemu-devel/2019-10/msg00738.html

Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Laurent Vivier]

Le 28/01/2020 à 10:26, Peter Maydell a écrit :
> On Thu, 16 Jan 2020 at 11:58, Matus Kysel <mkysel@tachyum.com> wrote:
>>
>> Used same style to handle another glibc reserved signal SIGSETXID (33),
>> that is used by glibc NPTL setuid/setgid functions. This should fix problems
>> with application using those functions and failing with error
>> "qemu:handle_cpu_signal received signal outside vCPU context".
>>
>> Signed-off-by: Matus Kysel <mkysel@tachyum.com>
>> ---
>>  linux-user/signal.c | 13 +++++++++----
>>  1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/linux-user/signal.c b/linux-user/signal.c
>> index 0128bde4d2..c59221fd0a 100644
>> --- a/linux-user/signal.c
>> +++ b/linux-user/signal.c
>> @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>>      [SIGPWR] = TARGET_SIGPWR,
>>      [SIGSYS] = TARGET_SIGSYS,
>>      /* next signals stay the same */
>> -    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
>> -       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-/
>> -       To fix this properly we need to do manual signal delivery multiplexed
>> -       over a single host signal.  */
>> +    /*
>> +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and SIGRTMAX - 1
>> +     * to avoid overlap with host libpthread (NPTL glibc) signals.
>> +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
>> +     * To fix this properly we need to do manual signal delivery multiplexed
>> +     * over a single host signal.
>> +     */
>>      [__SIGRTMIN] = __SIGRTMAX,
>> +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
>> +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
>>      [__SIGRTMAX] = __SIGRTMIN,
>>  };
>>  static uint8_t target_to_host_signal_table[_NSIG];
>> --
>> 2.17.1
> 
> This is a long-standing known problem, but doing this is likely
> to break currently-working guest binaries (notably things written
> in Go). See for example the discussion on this thread:
> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html

Peter,

I try to fix this problem and I'd like to find a reproducer for the Go
problem.

I tried to write an "hello world" program and run it in an arm64/bionic
chroot but there is no problem (with and without this patch).

Any hints?

Thanks,
Laurent

Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Laurent Vivier]

Le 29/01/2020 à 17:12, Laurent Vivier a écrit :
> Le 28/01/2020 à 10:26, Peter Maydell a écrit :
>> On Thu, 16 Jan 2020 at 11:58, Matus Kysel <mkysel@tachyum.com> wrote:
>>>
>>> Used same style to handle another glibc reserved signal SIGSETXID (33),
>>> that is used by glibc NPTL setuid/setgid functions. This should fix problems
>>> with application using those functions and failing with error
>>> "qemu:handle_cpu_signal received signal outside vCPU context".
>>>
>>> Signed-off-by: Matus Kysel <mkysel@tachyum.com>
>>> ---
>>>  linux-user/signal.c | 13 +++++++++----
>>>  1 file changed, 9 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/linux-user/signal.c b/linux-user/signal.c
>>> index 0128bde4d2..c59221fd0a 100644
>>> --- a/linux-user/signal.c
>>> +++ b/linux-user/signal.c
>>> @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>>>      [SIGPWR] = TARGET_SIGPWR,
>>>      [SIGSYS] = TARGET_SIGSYS,
>>>      /* next signals stay the same */
>>> -    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
>>> -       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-/
>>> -       To fix this properly we need to do manual signal delivery multiplexed
>>> -       over a single host signal.  */
>>> +    /*
>>> +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and SIGRTMAX - 1
>>> +     * to avoid overlap with host libpthread (NPTL glibc) signals.
>>> +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
>>> +     * To fix this properly we need to do manual signal delivery multiplexed
>>> +     * over a single host signal.
>>> +     */
>>>      [__SIGRTMIN] = __SIGRTMAX,
>>> +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
>>> +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
>>>      [__SIGRTMAX] = __SIGRTMIN,
>>>  };
>>>  static uint8_t target_to_host_signal_table[_NSIG];
>>> --
>>> 2.17.1
>>
>> This is a long-standing known problem, but doing this is likely
>> to break currently-working guest binaries (notably things written
>> in Go). See for example the discussion on this thread:
>> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html
> 
> Peter,
> 
> I try to fix this problem and I'd like to find a reproducer for the Go
> problem.
> 
> I tried to write an "hello world" program and run it in an arm64/bionic
> chroot but there is no problem (with and without this patch).
> 
> Any hints?

Markus has sent me the information.

I'm able to reproduce the problem with an "Hello World" go program and
go 1.10 (basically ubuntu bionic/arm64).

Thanks,
Laurent