Fix handling of compat_siginfo_t

The current handling of compat_siginfo_t is a mess: each architecture has its own implementation, all of which are incorrect in different ways. This patch series replaces all of the arch-specific versions with a single generic one that is guaranteed to produce the same results as a 32-bit kernel.

Most architectures are able to use the generic compat_siginfo_t, except x86 and MIPS. MIPS uses a slightly different compat_siginfo_t structure for ABI reasons but can still use the generic copy_siginfo_{to,from}_user32. x86 can't use the generic versions because it needs special handling for __SI_CHLD for x32 tasks.

One issue that isn't resolved in this series is sending signals between a 32-bit process and 64-bit process. Sending a si_int will work correctly, but a si_ptr value will likely get corrupted due to the different layouts of the 32-bit and 64-bit siginfo_t structures.

signalfd_copyinfo was also modified to properly generate data for compat tasks. In particular the ssi_ptr and ssi_data members need to be sign-extended to 64 bits rather than zero-extended, since that is the behavior in 32-bit kernels.

This series has been tested on x86_64 and arm64.

Changes since v1:
- Properly copy padding bytes and avoid leaking uninitialized data to userspace
- Fixed compile errors on mips and powerpc
- Fixed some compiler warnings
- Fixed some formatting issues

Amanieu d'Antras (20):
compat: Add generic compat_siginfo_t
compat: Add generic copy_siginfo_{to,from}_user32
x86: Update compat_siginfo_t to be closer to the generic version
x86: Rewrite copy_siginfo_{to,from}_user32
mips: Clean up compat_siginfo_t
mips: Use generic copy_siginfo_{to,from}_user32
arm64: Use generic compat_siginfo_t
arm64: Use generic copy_siginfo_{to,from}_user32
parisc: Use generic compat_siginfo_t
parsic: Use generic copy_siginfo_{to,from}_user32
s390: Use generic compat_siginfo_t
s390: Use generic copy_siginfo_{to,from}_user32
powerpc: Use generic compat_siginfo_t
powerpc: Use generic copy_siginfo_{to,from}_user32
tile: Use generic compat_siginfo_t
tile: Use generic copy_siginfo_{to,from}_user32
sparc: Use generic compat_siginfo_t
sparc: Use generic copy_siginfo_{to,from}_user32
signalfd: Fix some issues in signalfd_copyinfo
signal: Remove unnecessary zero-initialization of siginfo_t

 arch/arm64/include/asm/compat.h    |  59 --------
 arch/arm64/kernel/signal32.c       |  85 -----------
 arch/mips/include/asm/compat.h     |  63 ++++----
 arch/mips/kernel/signal32.c        |  62 --------
 arch/parisc/include/asm/compat.h   |  52 -------
 arch/parisc/kernel/signal32.c      | 102 -------------
 arch/powerpc/include/asm/compat.h  |  60 --------
 arch/powerpc/kernel/signal_32.c    |  72 +---------
 arch/s390/include/asm/compat.h     |  51 -------
 arch/s390/kernel/compat_signal.c   | 102 -------------
 arch/sparc/include/asm/compat.h    |  54 -------
 arch/sparc/kernel/signal32.c       |  69 ---------
 arch/tile/include/asm/compat.h     |  57 --------
 arch/tile/kernel/compat_signal.c   |  75 ----------
 arch/x86/include/asm/compat.h      |  39 +++--
 arch/x86/kernel/signal_compat.c    | 285 ++++++++++++++++++++++++++++---------
 fs/signalfd.c                      |  58 +++++---
 include/linux/compat.h             |  66 ++++++++-
 include/uapi/asm-generic/siginfo.h |   1 +
 kernel/compat.c                    | 224 +++++++++++++++++++++++++++++
 kernel/ptrace.c                    |   1 -
 kernel/signal.c                    |  16 ++-
 22 files changed, 615 insertions(+), 1038 deletions(-)

2.6.2