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From bc26025ccc64a2a63fc58776c93e2e4392445abe Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@parabola.nu>
Date: Wed, 27 Dec 2017 19:44:00 -0500
Subject: [PATCH 04/10] linux-user: init_guest_space: Correctly handle
guest_start in commpage initialization
init_guest_commpage needs to check if the mapped space, which ends at
real_start+real_size overlaps with where it needs to put the commpage,
which is (assuming sane qemu_host_page_size) guest_base + 0xffff000, where
guest_base is real_start - guest_start.
[guest_base][ 0xffff0000 ][commpage]
[guest_base][guest_start][real_size] [commpage]
[ real_start ][real_size] [commpage]
^
fail if this gap < 0
Since init_guest_commpage wants to do everything relative to guest_base
(rather than real_start), it obviously needs to be comparing 0xffff0000
against guest_start+real_size, not just real_size.
This bug has been present since 806d102141b99d4f1e55a97d68b7ea8c8ba3129f in
2012, but guest_start is usually 0, and prior to v2.11 real_size was
usually much smaller than 0xffff0000, so it was uncommon for it to have
made a difference.
Signed-off-by: Luke Shumaker <lukeshu@parabola.nu>
---
linux-user/elfload.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 1a6b660b25..f41cecc3cb 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1882,7 +1882,7 @@ unsigned long init_guest_space(unsigned long host_start,
#if defined(TARGET_ARM) && !defined(TARGET_AARCH64)
/* On 32-bit ARM, we need to also be able to map the commpage. */
int valid = init_guest_commpage(real_start - guest_start,
- real_size);
+ real_size + guest_start);
if (valid == 1) {
break;
} else if (valid == -1) {
--
2.15.1
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