From 2667e069e7b5807c69f32109d930967bc1b222cb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alex=20Benn=C3=A9e?= Date: Fri, 24 Jul 2020 07:45:01 +0100 Subject: [PATCH] linux-user: don't use MAP_FIXED in pgd_find_hole_fallback MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Plain MAP_FIXED has the undesirable behaviour of splatting exiting maps so we don't actually achieve what we want when looking for gaps. We should be using MAP_FIXED_NOREPLACE. As this isn't always available we need to potentially check the returned address to see if the kernel gave us what we asked for. Fixes: ad592e37dfc ("linux-user: provide fallback pgd_find_hole for bare chroots") Signed-off-by: Alex Bennée Reviewed-by: Richard Henderson Message-Id: <20200724064509.331-9-alex.bennee@linaro.org> --- include/qemu/osdep.h | 3 +++ linux-user/elfload.c | 10 ++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index 0b1298b3c9..20872e793e 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -173,6 +173,9 @@ extern int daemon(int, int); #ifndef MAP_ANONYMOUS #define MAP_ANONYMOUS MAP_ANON #endif +#ifndef MAP_FIXED_NOREPLACE +#define MAP_FIXED_NOREPLACE 0 +#endif #ifndef ENOMEDIUM #define ENOMEDIUM ENODEV #endif diff --git a/linux-user/elfload.c b/linux-user/elfload.c index 7e7f642332..fe9dfe795d 100644 --- a/linux-user/elfload.c +++ b/linux-user/elfload.c @@ -2134,12 +2134,15 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk, /* we have run out of space */ return -1; } else { - int flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE | MAP_FIXED; + int flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE | + MAP_FIXED_NOREPLACE; void * mmap_start = mmap((void *) align_start, guest_size, PROT_NONE, flags, -1, 0); if (mmap_start != MAP_FAILED) { munmap((void *) align_start, guest_size); - return (uintptr_t) mmap_start + offset; + if (MAP_FIXED_NOREPLACE || mmap_start == (void *) align_start) { + return (uintptr_t) mmap_start + offset; + } } base += qemu_host_page_size; } @@ -2307,9 +2310,8 @@ static void pgb_reserved_va(const char *image_name, abi_ulong guest_loaddr, /* Widen the "image" to the entire reserved address space. */ pgb_static(image_name, 0, reserved_va, align); -#ifdef MAP_FIXED_NOREPLACE + /* osdep.h defines this as 0 if it's missing */ flags |= MAP_FIXED_NOREPLACE; -#endif /* Reserve the memory on the host. */ assert(guest_base != 0);