[PATCH v2] linux-user: Tolerate CONFIG_LSM_MMAP_MIN_ADDR

[PATCH v2] linux-user: Tolerate CONFIG_LSM_MMAP_MIN_ADDR

[Ilya Leoshkevich]

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.

Closes: https://gitlab.com/qemu-project/qemu/-/issues/2598
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
v1: https://lore.kernel.org/qemu-devel/20241021121820.483535-1-iii@linux.ibm.com/
v1 -> v2: Start looking for a suitable hole from a higher address,
          instead of falling back to probing (Richard).

 linux-user/elfload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 6cef8db3b53..d6ad77d27dc 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) {
-- 
2.47.0

Re: [PATCH v2] linux-user: Tolerate CONFIG_LSM_MMAP_MIN_ADDR

[Richard Henderson]

On 10/22/24 17:24, Ilya Leoshkevich wrote:
> 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.
> 
> Closes: https://gitlab.com/qemu-project/qemu/-/issues/2598
> Suggested-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
> v1: https://lore.kernel.org/qemu-devel/20241021121820.483535-1-iii@linux.ibm.com/
> v1 -> v2: Start looking for a suitable hole from a higher address,
>            instead of falling back to probing (Richard).
> 
>   linux-user/elfload.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 6cef8db3b53..d6ad77d27dc 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) {

Queued, thanks.

r~