Re: [PATCH] linux-user: fix bug about incorrect base addresss of idt and gdt on i386 and x86_64

[Alex Bennée]

fanwj@mail.ustc.edu.cn writes:

> From 4601a624f40b2c89e7df2dec1adffb4f4308ba2d Mon Sep 17 00:00:00 2001
> From: fanwenjie <fanwj@mail.ustc.edu.cn>
> Date: Sun, 1 Jan 2023 23:13:34 +0800
> Subject: [PATCH] linux-user: fix bug about incorrect base addresss of idt and
>  gdt on i386 and x86_64
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1405
> Signed-off-by: fanwenjie <fanwj@mail.ustc.edu.cn>
> ---
>  linux-user/main.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index a17fed045b..5d673c95b3 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -171,6 +171,12 @@ void fork_end(int child)
>  
>  __thread CPUState *thread_cpu;
>  
> +#if defined(TARGET_I386) || defined(TARGET_X86_64)
> +#include <stdalign.h>
> +__thread alignas(TARGET_PAGE_SIZE) static uint64_t 
> gdt_base[TARGET_GDT_ENTRIES];
> +__thread alignas(TARGET_PAGE_SIZE) static uint64_t idt_base[TARGET_PAGE_SIZE 
> / sizeof(uint64_t)];
> +#endif
> +
>  bool qemu_cpu_is_self(CPUState *cpu)
>  {
>      return thread_cpu == cpu;
> @@ -235,6 +241,13 @@ CPUArchState *cpu_copy(CPUArchState *env)
>      new_cpu->tcg_cflags = cpu->tcg_cflags;
>      memcpy(new_env, env, sizeof(CPUArchState));
>  
> +#if defined(TARGET_I386) || defined(TARGET_X86_64)
> +    memcpy(idt_base, (void*)new_env->idt.base, sizeof(uint64_t) * 
> (new_env->idt.limit + 1));
> +    memcpy(gdt_base, (void*)new_env->gdt.base, sizeof(uint64_t) * 
> TARGET_GDT_ENTRIES);
> +    new_env->idt.base = (target_ulong)idt_base;
> +    new_env->gdt.base = (target_ulong)gdt_base;
> +#endif
> +

This is the wrong place to copy target specific bits of code. I think
this belongs with cpu_clone_regs_child and the gdt/idt structures in
linux-user/i386/cpu_loop.c I think.

>      /* Clone all break/watchpoints.
>         Note: Once we support ptrace with hw-debug register access, make sure
>         BP_CPU break/watchpoints are handled correctly on clone. */


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro