From 6e53a62a0d529fb5cf8df8304ef02b691fb2736c Mon Sep 17 00:00:00 2001
From: Dave Martin <Dave.Martin@arm.com>
Date: Wed, 18 Jan 2017 16:25:24 +0000
Subject: arm64/ptrace: Reject attempts to set incomplete hardware breakpoint
 fields

commit ad9e202aa1ce571b1d7fed969d06f66067f8a086 upstream.

We cannot preserve partial fields for hardware breakpoints, because
the values written by userspace to the hardware breakpoint
registers can't subsequently be recovered intact from the hardware.

So, just reject attempts to write incomplete fields with -EINVAL.

Fixes: 478fcb2cdb23 ("arm64: Debugging support")
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <Will.Deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 143f770..8eedeef 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -550,6 +550,8 @@ static int hw_break_set(struct task_struct *target,
 	/* (address, ctrl) registers */
 	limit = regset->n * regset->size;
 	while (count && offset < limit) {
+		if (count < PTRACE_HBP_ADDR_SZ)
+			return -EINVAL;
 		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &addr,
 					 offset, offset + PTRACE_HBP_ADDR_SZ);
 		if (ret)
@@ -559,6 +561,8 @@ static int hw_break_set(struct task_struct *target,
 			return ret;
 		offset += PTRACE_HBP_ADDR_SZ;
 
+		if (!count)
+			break;
 		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &ctrl,
 					 offset, offset + PTRACE_HBP_CTRL_SZ);
 		if (ret)
-- 
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