linux-kernel - [PATCH AUTOSEL for 3.18 057/101] arm64: ptrace: Avoid setting compat FP[SC]R to garbage if get

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Message-ID: <20180409004042.164920-7-alexander.levin@microsoft.com>
Date:   Mon, 9 Apr 2018 00:41:21 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Dave Martin <Dave.Martin@....com>,
        Will Deacon <will.deacon@....com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 3.18 057/101] arm64: ptrace: Avoid setting compat
 FP[SC]R to garbage if get_user fails

From: Dave Martin <Dave.Martin@....com>

[ Upstream commit 53b1a742ed251780267a57415bc955bd50f40c3d ]

If get_user() fails when reading the new FPSCR value from userspace
in compat_vfp_get(), then garbage* will be written to the task's
FPSR and FPCR registers.

This patch prevents this by checking the return from get_user()
first.

[*] Actually, zero, due to the behaviour of get_user() on error, but
that's still not what userspace expects.

Fixes: 478fcb2cdb23 ("arm64: Debugging support")
Signed-off-by: Dave Martin <Dave.Martin@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 arch/arm64/kernel/ptrace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 2e845f5c8ab2..a12eb17e7985 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -785,8 +785,10 @@ static int compat_vfp_set(struct task_struct *target,
 
 	if (count && !ret) {
 		ret = get_user(fpscr, (compat_ulong_t *)ubuf);
-		uregs->fpsr = fpscr & VFP_FPSCR_STAT_MASK;
-		uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
+		if (!ret) {
+			uregs->fpsr = fpscr & VFP_FPSCR_STAT_MASK;
+			uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
+		}
 	}
 
 	fpsimd_flush_task_state(target);
-- 
2.15.1