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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Dave Martin <Dave.Martin@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 121/293] arm64: ptrace: Fix VFP register
 dumping in compat coredumps
Thread-Topic: [PATCH AUTOSEL for 4.9 121/293] arm64: ptrace: Fix VFP register
 dumping in compat coredumps
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Date:   Mon, 9 Apr 2018 00:24:27 +0000
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From: Dave Martin <Dave.Martin@arm.com>

[ Upstream commit af66b2d88a76574d55e81d712292abd34beb6178 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 arch/arm64/kernel/ptrace.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index d1fd560b3a2a..5c78b64369cf 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -896,7 +896,7 @@ static int compat_vfp_get(struct task_struct *target,
 {
 	struct user_fpsimd_state *uregs;
 	compat_ulong_t fpscr;
-	int ret;
+	int ret, vregs_end_pos;
=20
 	uregs =3D &target->thread.fpsimd_state.user_fpsimd;
=20
@@ -904,13 +904,16 @@ static int compat_vfp_get(struct task_struct *target,
 	 * 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.
 	 */
-	ret =3D user_regset_copyout(&pos, &count, &kbuf, &ubuf, uregs, 0,
-				  VFP_STATE_SIZE - sizeof(compat_ulong_t));
+	vregs_end_pos =3D VFP_STATE_SIZE - sizeof(compat_ulong_t);
+	ret =3D user_regset_copyout(&pos, &count, &kbuf, &ubuf, uregs,
+				  0, vregs_end_pos);
=20
 	if (count && !ret) {
 		fpscr =3D (uregs->fpsr & VFP_FPSCR_STAT_MASK) |
 			(uregs->fpcr & VFP_FPSCR_CTRL_MASK);
-		ret =3D put_user(fpscr, (compat_ulong_t *)ubuf);
+
+		ret =3D user_regset_copyout(&pos, &count, &kbuf, &ubuf, &fpscr,
+					  vregs_end_pos, VFP_STATE_SIZE);
 	}
=20
 	return ret;
--=20
2.15.1