Rust, i386, accelerator changes for 2025-10-14

[PULL 14/28] target/i386: user: do not set up a valid LDT on reset

Paolo Bonzini posted 28 patches 1 month ago

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Maintainers: Paolo Bonzini <pbonzini@redhat.com>, "Dr. David Alan Gilbert" <dave@treblig.org>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Yanan Wang <wangyanan55@huawei.com>, Zhao Liu <zhao1.liu@intel.com>, "Michael S. Tsirkin" <mst@redhat.com>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Manos Pitsidianakis <manos.pitsidianakis@linaro.org>, Peter Maydell <peter.maydell@linaro.org>, Marcelo Tosatti <mtosatti@redhat.com>, Song Gao <gaosong@loongson.cn>, Huacai Chen <chenhuacai@kernel.org>, Aurelien Jarno <aurelien@aurel32.net>, Jiaxun Yang <jiaxun.yang@flygoat.com>, Aleksandar Rikalo <arikalo@gmail.com>, Nicholas Piggin <npiggin@gmail.com>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Chinmay Rath <rathc@linux.ibm.com>, Palmer Dabbelt <palmer@dabbelt.com>, Alistair Francis <alistair.francis@wdc.com>, Weiwei Li <liwei1518@gmail.com>, Daniel Henrique Barboza <dbarboza@ventanamicro.com>, Liu Zhiwei <zhiwei_liu@linux.alibaba.com>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, Matthew Rosato <mjrosato@linux.ibm.com>, Thomas Huth <thuth@redhat.com>, David Hildenbrand <david@redhat.com>, Ilya Leoshkevich <iii@linux.ibm.com>, Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <fam@euphon.net>

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[PULL 14/28] target/i386: user: do not set up a valid LDT on reset

Posted by Paolo Bonzini 1 month ago

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>
---
 target/i386/cpu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 4f99cbc5c0b..455caff6b23 100644
--- 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);
-- 
2.51.0