target/i386: user: do not set up a valid LDT on reset

In user-mode emulation, QEMU uses the default setting of the LDT base
and limit, which places it at the bottom 64K of virtual address space.
However, by default there is no LDT at all in Linux processes, and
therefore the limit should be 0.

This is visible as a NULL pointer dereference in LSL and LAR instructions
when they try to read the LDT at an unmapped address.

Resolves: #1376
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 4f99cbc5c0b70594313c956836a39c6334a96f6c..455caff6b2305456bb1838c2a6b573bceee2fbe9 100644 (file)
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -8649,7 +8649,11 @@ static void x86_cpu_reset_hold(Object *obj, ResetType type)
 
     env->idt.limit = 0xffff;
     env->gdt.limit = 0xffff;
+#if defined(CONFIG_USER_ONLY)
+    env->ldt.limit = 0;
+#else
     env->ldt.limit = 0xffff;
+#endif
     env->ldt.flags = DESC_P_MASK | (2 << DESC_TYPE_SHIFT);
     env->tr.limit = 0xffff;
     env->tr.flags = DESC_P_MASK | (11 << DESC_TYPE_SHIFT);