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linux-user: don't use MAP_FIXED in pgd_find_hole_fallback

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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: ad592e37df ("linux-user: provide fallback pgd_find_hole for bare chroots")
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200724064509.331-9-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée 2020-07-24 07:45:01 +01:00
parent 163b3d1af2
commit 2667e069e7
2 changed files with 9 additions and 4 deletions
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3
include/qemu/osdep.h
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@ -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

10
linux-user/elfload.c
View File

@ -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);