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arm64: ptrace: Fix VFP register dumping in compat coredumps

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Currently, VFP registers are omitted from coredumps for compat
processes, due to a bug in the REGSET_COMPAT_VFP regset
implementation.

compat_vfp_get() needs to transfer non-contiguous data from
thread_struct.fpsimd_state, and uses put_user() to handle the
offending trailing word (FPSCR).  This fails when copying to a
kernel address (i.e., kbuf && !ubuf), which is what happens when
dumping core.  As a result, the ELF coredump core code silently
omits the NT_ARM_VFP note from the dump.

It would be possible to work around this with additional special
case code for the put_user(), but since user_regset_copyout() is
explicitly designed to handle this scenario it is cleaner to port
the put_user() to a user_regset_copyout() call, which this patch
does.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Dave Martin 2017-06-21 16:00:42 +01:00 • committed by Will Deacon
parent f5d284900c
commit af66b2d88a
1 changed files with 7 additions and 4 deletions
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11
arch/arm64/kernel/ptrace.c
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@ -894,7 +894,7 @@ static int compat_vfp_get(struct task_struct *target,
{ {
struct user_fpsimd_state *uregs; struct user_fpsimd_state *uregs;
compat_ulong_t fpscr; compat_ulong_t fpscr;
int ret; int ret, vregs_end_pos;
uregs = &target->thread.fpsimd_state.user_fpsimd; uregs = &target->thread.fpsimd_state.user_fpsimd;
@ -902,13 +902,16 @@ static int compat_vfp_get(struct task_struct *target,
* The VFP registers are packed into the fpsimd_state, so they all sit * The VFP registers are packed into the fpsimd_state, so they all sit
* nicely together for us. We just need to create the fpscr separately. * nicely together for us. We just need to create the fpscr separately.
*/ */
ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, uregs, 0, vregs_end_pos = VFP_STATE_SIZE - sizeof(compat_ulong_t);
VFP_STATE_SIZE - sizeof(compat_ulong_t)); ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, uregs,
0, vregs_end_pos);
if (count && !ret) { if (count && !ret) {
fpscr = (uregs->fpsr & VFP_FPSCR_STAT_MASK) | fpscr = (uregs->fpsr & VFP_FPSCR_STAT_MASK) |
(uregs->fpcr & VFP_FPSCR_CTRL_MASK); (uregs->fpcr & VFP_FPSCR_CTRL_MASK);
ret = put_user(fpscr, (compat_ulong_t *)ubuf);
ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &fpscr,
vregs_end_pos, VFP_STATE_SIZE);
} }
return ret; return ret;