linux-kernel - [PATCH] x86/e820: set end to (start + size

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Date:   Sat, 20 Aug 2016 01:40:13 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     tglx@...utronix.de, yinghai@...nel.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH] x86/e820: set end to (start + size - 1) in __append_e820_map()

The (start, size) tuple represents a range [start, start + size - 1],
which means "start" and "start + size - 1" should be compared to see
whether the range overflows.

For example, a range with (start, size)

	(0xffffffff fffffff0, 0x00000000 00000010)

represents

	[0xffffffff fffffff0, 0xffffffff ffffffff]

would be judged overflow in the original code, while actually it is not.

This patch fixes this and makes sure it still works when size is zero.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
---
 arch/x86/kernel/e820.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 621b501..871f186 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -388,11 +388,11 @@ static int __init __append_e820_map(struct e820entry *biosmap, int nr_map)
 	while (nr_map) {
 		u64 start = biosmap->addr;
 		u64 size = biosmap->size;
-		u64 end = start + size;
+		u64 end = start + size - 1;
 		u32 type = biosmap->type;
 
 		/* Overflow in 64 bits? Ignore the memory map. */
-		if (start > end)
+		if (start > end && likely(size))
 			return -1;
 
 		e820_add_region(start, size, type);
-- 
1.7.9.5