linux-toradex.git/arch/x86/include/uapi/asm/sigcontext.h, branch v4.10

x86/signal/64: Re-add support for SS in the 64-bit signal context

2016-02-17T07:32:11+00:00

This is a second attempt to make the improvements from c6f2062935c8
("x86/signal/64: Fix SS handling for signals delivered to 64-bit
programs"), which was reverted by 51adbfbba5c6 ("x86/signal/64: Add
support for SS in the 64-bit signal context").

This adds two new uc_flags flags.  UC_SIGCONTEXT_SS will be set for
all 64-bit signals (including x32).  It indicates that the saved SS
field is valid and that the kernel supports the new behavior.

The goal is to fix a problems with signal handling in 64-bit tasks:
SS wasn't saved in the 64-bit signal context, making it awkward to
determine what SS was at the time of signal delivery and making it
impossible to return to a non-flat SS (as calling sigreturn clobbers
SS).

This also made it extremely difficult for 64-bit tasks to return to
fully-defined 16-bit contexts, because only the kernel can easily do
espfix64, but sigreturn was unable to set a non-flag SS:ESP.
(DOSEMU has a monstrous hack to partially work around this
limitation.)

If we could go back in time, the correct fix would be to make 64-bit
signals work just like 32-bit signals with respect to SS: save it
in signal context, reset it when delivering a signal, and restore
it in sigreturn.

Unfortunately, doing that (as I tried originally) breaks DOSEMU:
DOSEMU wouldn't reset the signal context's SS when clearing the LDT
and changing the saved CS to 64-bit mode, since it predates the SS
context field existing in the first place.

This patch is a bit more complicated, and it tries to balance a
bunch of goals.  It makes most cases of changing ucontext->ss during
signal handling work as expected.

I do this by special-casing the interesting case.  On sigreturn,
ucontext->ss will be honored by default, unless the ucontext was
created from scratch by an old program and had a 64-bit CS
(unfortunately, CRIU can do this) or was the result of changing a
32-bit signal context to 64-bit without resetting SS (as DOSEMU
does).

For the benefit of new 64-bit software that uses segmentation (new
versions of DOSEMU might), the new behavior can be detected with a
new ucontext flag UC_SIGCONTEXT_SS.

To avoid compilation issues, __pad0 is left as an alias for ss in
ucontext.

The nitty-gritty details are documented in the header file.

This patch also re-enables the sigreturn_64 and ldt_gdt_64 selftests,
as the kernel change allows both of them to pass.

Tested-by: Stas Sergeev 
Signed-off-by: Andy Lutomirski 
Acked-by: Borislav Petkov 
Cc: Al Viro 
Cc: Andy Lutomirski 
Cc: Brian Gerst 
Cc: Cyrill Gorcunov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Pavel Emelyanov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/749149cbfc3e75cd7fcdad69a854b399d792cc6f.1455664054.git.luto@kernel.org
[ Small readability edit. ]
Signed-off-by: Ingo Molnar

x86/signal/64: Add a comment about sigcontext->fs and gs

2016-02-17T07:32:11+00:00

These fields have a strange history.  This tries to document it.

This borrows from 9a036b93a344 ("x86/signal/64: Remove 'fs' and 'gs'
from sigcontext"), which was reverted by ed596cde9425 ("Revert x86
sigcontext cleanups").

Signed-off-by: Andy Lutomirski 
Acked-by: Borislav Petkov 
Cc: Al Viro 
Cc: Andy Lutomirski 
Cc: Brian Gerst 
Cc: Cyrill Gorcunov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Pavel Emelyanov 
Cc: Peter Zijlstra 
Cc: Stas Sergeev 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/baa78f3c84106fa5acbc319377b1850602f5deec.1455664054.git.luto@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Clean up too long lines

2015-09-14T09:09:33+00:00

Signed-off-by: Peter Zijlstra 
Cc: Linus Torvalds 
Cc: Thomas Gleixner 
Cc: bp@alien8.de
Cc: brgerst@gmail.com
Cc: dvlasenk@redhat.com
Cc: luto@amacapital.net
Cc: mikko.rapeli@iki.fi
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/20150909071244.GM3644@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar

x86/headers: Convert sigcontext_ia32 uses to sigcontext_32

2015-09-08T08:03:59+00:00

Use the new name in kernel code, and move the old name to the
user-space-only legacy section of the UAPI header.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-14-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Unify 'struct sigcontext_ia32' and 'struct sigcontext_32'

2015-09-08T08:03:58+00:00

The two structures are identical - merge them and keep the
legacy name as a define.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-13-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Make sigcontext pointers bit independent

2015-09-08T08:03:58+00:00

Before we can eliminate the duplication between 'struct
sigcontext_32' and 'struct sigcontext_ia32', make the 'fpstate'
pointer field in 'struct sigcontext_32' bit independent.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-12-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Move the 'struct sigcontext' definitions into the UAPI header

2015-09-08T08:03:58+00:00

Our goal is to eliminate the duplicate struct sigcontext_ia32
definition, so move the kernel's primary sigcontext type into
the UAPI header, defining these two variants:

	struct sigcontext_32
	struct sigcontext_64

... and map them to 'struct sigcontext'.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-11-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Convert uses of _fpstate_ia32 to _fpstate_32

2015-09-08T08:03:57+00:00

Remove uses of _fpstate_ia32 from the kernel, and move the
legacy _fpstate_ia32 definition to the user-space only portion
of the header.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-9-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Unify 'struct _fpstate_ia32' and i386 struct _fpstate

2015-09-08T08:03:57+00:00

'struct _fpstate_ia32' and 'struct _fpstate' on i386 are
identical in all fields, except 'padding1' being named
'padding'.

We unify the two structures and add a union that is both named
'padding1' and 'padding', in the (unlikely) case there's
user-space code that relies on the padding field name.

We rename the two main types to be:

  struct _fpstate_32
  struct _fpstate_64

for the 32-bit and 64-bit frame, and map them to the main and
compat structure names (_fpstate) depending on whether we are on
32-bit or on 64-bit kernels.

We also keep the old _fpstate_ia32 name as a legacy name.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-8-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar

x86/headers: Unify register type definitions between 32-bit compat and i386

2015-09-08T08:03:56+00:00

The following sigcontext related types were duplicated across
native 32-bit and compat 32-bit headers:

  struct _fpreg;
  struct _fpxreg;
  struct _xmmreg;

  X86_FXSR_MAGIC

Unify them.

Acked-by: Mikko Rapeli 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-7-git-send-email-mingo@kernel.org
Signed-off-by: Ingo Molnar