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[PATCH v3 08/16] linux-user: don't use MAP_FIXED in pgd_find_hole_fallba
From: |
Alex Bennée |
Subject: |
[PATCH v3 08/16] linux-user: don't use MAP_FIXED in pgd_find_hole_fallback |
Date: |
Fri, 24 Jul 2020 07:45:01 +0100 |
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 <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200722062902.24509-9-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 0b1298b3c91..20872e793e4 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 7e7f642332d..fe9dfe795dd 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);
--
2.20.1
- [PATCH v3 00/16] candidate fixes for 5.1-rc1 (testing, semihosting, OOM tcg, x86 fpu), Alex Bennée, 2020/07/24
- [PATCH v3 03/16] semihosting: don't send the trailing '\0', Alex Bennée, 2020/07/24
- [PATCH v3 01/16] shippable: add one more qemu to registry url, Alex Bennée, 2020/07/24
- [PATCH v3 02/16] semihosting: defer connect_chardevs a little more to use serialx, Alex Bennée, 2020/07/24
- [PATCH v3 04/16] util: add qemu_get_host_physmem utility function, Alex Bennée, 2020/07/24
- [PATCH v3 06/16] accel/tcg: better handle memory constrained systems, Alex Bennée, 2020/07/24
- [PATCH v3 05/16] util/oslib-win32: add qemu_get_host_physmem implementation, Alex Bennée, 2020/07/24
- [PATCH v3 08/16] linux-user: don't use MAP_FIXED in pgd_find_hole_fallback,
Alex Bennée <=
- [PATCH v3 10/16] tests/docker: fix binfmt_misc image building, Alex Bennée, 2020/07/24
- [PATCH v3 07/16] target/i386: floatx80: avoid compound literals in static initializers, Alex Bennée, 2020/07/24
- [PATCH v3 12/16] linux-user: fix clock_nanosleep(), Alex Bennée, 2020/07/24
- [PATCH v3 16/16] tests/vm: add shutdown timeout in basevm.py, Alex Bennée, 2020/07/24
- [PATCH v3 11/16] tests/docker: add support for DEB_KEYRING, Alex Bennée, 2020/07/24
- [PATCH v3 14/16] python/qemu: Cleanup changes to ConsoleSocket, Alex Bennée, 2020/07/24
- [PATCH v3 09/16] tests/docker: fix update command due to python3 str/bytes distinction, Alex Bennée, 2020/07/24