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

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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>
This commit is contained in:
Paolo Bonzini
2025-10-14 11:03:59 +02:00
parent 5142397c79
commit 58aa1d08bb
1 changed files with 4 additions and 0 deletions
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target/i386/cpu.c
+4
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@@ -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);