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arm64: compat: fix vfp save/restore across signal handlers in big-endian 

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.

Cc: <stable@vger.kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2015-09-15 12:07:06 +01:00
parent e56d82a116
commit bdec97a855
1 changed files with 36 additions and 11 deletions
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47
arch/arm64/kernel/signal32.c
View File

@ -212,14 +212,32 @@ int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
/*
* VFP save/restore code.
*
* We have to be careful with endianness, since the fpsimd context-switch
* code operates on 128-bit (Q) register values whereas the compat ABI
* uses an array of 64-bit (D) registers. Consequently, we need to swap
* the two halves of each Q register when running on a big-endian CPU.
*/
union __fpsimd_vreg {
__uint128_t raw;
struct {
#ifdef __AARCH64EB__
u64 hi;
u64 lo;
#else
u64 lo;
u64 hi;
#endif
};
};
static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
{
struct fpsimd_state *fpsimd = &current->thread.fpsimd_state;
compat_ulong_t magic = VFP_MAGIC;
compat_ulong_t size = VFP_STORAGE_SIZE;
compat_ulong_t fpscr, fpexc;
int err = 0;
int i, err = 0;
/*
* Save the hardware registers to the fpsimd_state structure.
@ -235,10 +253,15 @@ static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
/*
* Now copy the FP registers. Since the registers are packed,
* we can copy the prefix we want (V0-V15) as it is.
* FIXME: Won't work if big endian.
*/
err |= __copy_to_user(&frame->ufp.fpregs, fpsimd->vregs,
sizeof(frame->ufp.fpregs));
for (i = 0; i < ARRAY_SIZE(frame->ufp.fpregs); i += 2) {
union __fpsimd_vreg vreg = {
.raw = fpsimd->vregs[i >> 1],
};
__put_user_error(vreg.lo, &frame->ufp.fpregs[i], err);
__put_user_error(vreg.hi, &frame->ufp.fpregs[i + 1], err);
}
/* Create an AArch32 fpscr from the fpsr and the fpcr. */
fpscr = (fpsimd->fpsr & VFP_FPSCR_STAT_MASK) |
@ -263,7 +286,7 @@ static int compat_restore_vfp_context(struct compat_vfp_sigframe __user *frame)
compat_ulong_t magic = VFP_MAGIC;
compat_ulong_t size = VFP_STORAGE_SIZE;
compat_ulong_t fpscr;
int err = 0;
int i, err = 0;
__get_user_error(magic, &frame->magic, err);
__get_user_error(size, &frame->size, err);
@ -273,12 +296,14 @@ static int compat_restore_vfp_context(struct compat_vfp_sigframe __user *frame)
if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
return -EINVAL;
/*
* Copy the FP registers into the start of the fpsimd_state.
* FIXME: Won't work if big endian.
*/
err |= __copy_from_user(fpsimd.vregs, frame->ufp.fpregs,
sizeof(frame->ufp.fpregs));
/* Copy the FP registers into the start of the fpsimd_state. */
for (i = 0; i < ARRAY_SIZE(frame->ufp.fpregs); i += 2) {
union __fpsimd_vreg vreg;
__get_user_error(vreg.lo, &frame->ufp.fpregs[i], err);
__get_user_error(vreg.hi, &frame->ufp.fpregs[i + 1], err);
fpsimd.vregs[i >> 1] = vreg.raw;
}
/* Extract the fpsr and the fpcr from the fpscr */
__get_user_error(fpscr, &frame->ufp.fpscr, err);