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[PATCH] linux-user: Ensure mmap_min_addr is non-zero
From: |
Richard Henderson |
Subject: |
[PATCH] linux-user: Ensure mmap_min_addr is non-zero |
Date: |
Fri, 24 Jul 2020 14:23:14 -0700 |
When the chroot does not have /proc mounted, we can read neither
/proc/sys/vm/mmap_min_addr nor /proc/sys/maps.
The enforcement of mmap_min_addr in the host kernel is done by
the security module, and so does not apply to processes owned
by root. Which leads pgd_find_hole_fallback to succeed in probing
a reservation at address 0. Which confuses pgb_reserved_va to
believe that guest_base has not actually been initialized.
We don't actually want NULL addresses to become accessible, so
make sure that mmap_min_addr is initialized with a non-zero value.
Buglink: https://bugs.launchpad.net/qemu/+bug/1888728
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
linux-user/main.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/linux-user/main.c b/linux-user/main.c
index 3597e99bb1..75c9785157 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -758,14 +758,26 @@ int main(int argc, char **argv, char **envp)
if ((fp = fopen("/proc/sys/vm/mmap_min_addr", "r")) != NULL) {
unsigned long tmp;
- if (fscanf(fp, "%lu", &tmp) == 1) {
+ if (fscanf(fp, "%lu", &tmp) == 1 && tmp != 0) {
mmap_min_addr = tmp;
- qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n",
mmap_min_addr);
+ qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n",
+ mmap_min_addr);
}
fclose(fp);
}
}
+ /*
+ * We prefer to not make NULL pointers accessible to QEMU.
+ * If we're in a chroot with no /proc, fall back to 1 page.
+ */
+ if (mmap_min_addr == 0) {
+ mmap_min_addr = qemu_host_page_size;
+ qemu_log_mask(CPU_LOG_PAGE,
+ "host mmap_min_addr=0x%lx (fallback)\n",
+ mmap_min_addr);
+ }
+
/*
* Prepare copy of argv vector for target.
*/
--
2.25.1
- [PATCH] linux-user: Ensure mmap_min_addr is non-zero,
Richard Henderson <=