[PULL,03/14] linux-user: Tolerate CONFIG_LSM_MMAP_MIN_ADDR

Commit Message

Richard Henderson Nov. 15, 2024, 8:58 p.m. UTC

From: Ilya Leoshkevich <[e-mail]>

Running qemu-i386 on a system running with SELinux in enforcing mode
(more precisely: s390x trixie container on Fedora 40) fails with:

    qemu-i386: tests/tcg/i386-linux-user/sigreturn-sigmask: Unable to find a guest_base to satisfy all guest address mapping requirements
      00000000-ffffffff

The reason is that main() determines mmap_min_addr from
/proc/sys/vm/mmap_min_addr, but SELinux additionally defines
CONFIG_LSM_MMAP_MIN_ADDR, which is normally larger: 32K or 64K, but,
in general, can be anything. There is no portable way to query its
value: /boot/config, /proc/config and /proc/config.gz are distro- and
environment-specific.

Once the identity map fails, the magnitude of guest_base does not
matter, so fix by starting the search from 1M or 1G.

Cc: [e-mail]
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2598
Suggested-by: Richard Henderson <[e-mail]>
Signed-off-by: Ilya Leoshkevich <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Richard Henderson <[e-mail]>
---
 linux-user/elfload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 6cef8db3b5..d6ad77d27d 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2898,7 +2898,7 @@  static uintptr_t pgb_try_itree(const PGBAddrs *ga, uintptr_t base,
 static uintptr_t pgb_find_itree(const PGBAddrs *ga, IntervalTreeRoot *root,
                                 uintptr_t align, uintptr_t brk)
 {
-    uintptr_t last = mmap_min_addr;
+    uintptr_t last = sizeof(uintptr_t) == 4 ? MiB : GiB;
     uintptr_t base, skip;
 
     while (true) {