From bc26025ccc64a2a63fc58776c93e2e4392445abe Mon Sep 17 00:00:00 2001 From: Luke Shumaker 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 --- 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