[Qemu-devel] [PULL 5/5] linux-user: do setrlimit selectively

[Laurent Vivier]

From: Max Filippov <address@hidden>

setrlimit guest calls that affect memory resources
(RLIMIT_{AS,DATA,STACK}) may interfere with QEMU internal memory
management. They may result in QEMU lockup because mprotect call in
page_unprotect would fail with ENOMEM error code, causing infinite loop
of SIGSEGV. E.g. it happens when running libstdc++ testsuite for xtensa
target on x86_64 host.

Don't call host setrlimit for memory-related resources.

Reviewed-by: Peter Maydell <address@hidden>
Signed-off-by: Max Filippov <address@hidden>
Message-Id: <address@hidden>
[lv: rebase on master]
Signed-off-by: Laurent Vivier <address@hidden>
---
 linux-user/syscall.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 019af632df..ae3c0dfef7 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7879,7 +7879,21 @@ static abi_long do_syscall1(void *cpu_env, int num, 
abi_long arg1,
             rlim.rlim_cur = target_to_host_rlim(target_rlim->rlim_cur);
             rlim.rlim_max = target_to_host_rlim(target_rlim->rlim_max);
             unlock_user_struct(target_rlim, arg2, 0);
-            return get_errno(setrlimit(resource, &rlim));
+            /*
+             * If we just passed through resource limit settings for memory 
then
+             * they would also apply to QEMU's own allocations, and QEMU will
+             * crash or hang or die if its allocations fail. Ideally we would
+             * track the guest allocations in QEMU and apply the limits 
ourselves.
+             * For now, just tell the guest the call succeeded but don't 
actually
+             * limit anything.
+             */
+            if (resource != RLIMIT_AS &&
+                resource != RLIMIT_DATA &&
+                resource != RLIMIT_STACK) {
+                return get_errno(setrlimit(resource, &rlim));
+            } else {
+                return 0;
+            }
         }
 #endif
 #ifdef TARGET_NR_getrlimit
-- 
2.17.1