arm64: compat: fix vfp save/restore across signal handlers in big-endian
authorWill Deacon <will.deacon@arm.com>
Tue, 15 Sep 2015 11:07:06 +0000 (12:07 +0100)
committerDanny Wood <danwood76@gmail.com>
Tue, 29 Jan 2019 13:10:03 +0000 (13:10 +0000)
commit959bc253ee9b7b17310cb0f9752a13f028a40a96
treeff472d11801af24a2da1240d40607e67821cbdd1
parent65f5943699d6de36471c679381e2778ba5c4aa23
arm64: compat: fix vfp save/restore across signal handlers in big-endian

commit bdec97a855ef1e239f130f7a11584721c9a1bf04 upstream.

When saving/restoring the VFP registers from a compat (AArch32)
signal frame, we rely on the compat registers forming a prefix of the
native register file and therefore make use of copy_{to,from}_user to
transfer between the native fpsimd_state and the compat_vfp_sigframe.

Unfortunately, this doesn't work so well in a big-endian environment.
Our fpsimd save/restore code operates directly on 128-bit quantities
(Q registers) whereas the compat_vfp_sigframe represents the registers
as an array of 64-bit (D) registers. The architecture packs the compat D
registers into the Q registers, with the least significant bytes holding
the lower register. Consequently, we need to swap the 64-bit halves when
converting between these two representations on a big-endian machine.

This patch replaces the __copy_{to,from}_user invocations in our
compat VFP signal handling code with explicit __put_user loops that
operate on 64-bit values and swap them accordingly.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/arm64/kernel/signal32.c