Re: [Qemu-devel] [PATCH 09/43] windbg: handler of fs/gs register

[Ladi Prosek <lprosek@redhat.com>]

On Tue, Sep 26, 2017 at 1:04 PM, Mihail Abakumov
<mikhail.abakumov@ispras.ru> wrote:
> Added handler of fs/gs register. It tries to find and check KPCR and version address.
>
> Signed-off-by: Mihail Abakumov <mikhail.abakumov@ispras.ru>
> Signed-off-by: Pavel Dovgalyuk <dovgaluk@ispras.ru>
> Signed-off-by: Dmitriy Koltunov <koltunov@ispras.ru>
> ---
>  include/exec/windbgstub-utils.h |    5 +++
>  windbgstub-utils.c              |   63 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 66 insertions(+), 2 deletions(-)
>
> diff --git a/include/exec/windbgstub-utils.h b/include/exec/windbgstub-utils.h
> index 90fb766839..f2402ebb34 100755
> --- a/include/exec/windbgstub-utils.h
> +++ b/include/exec/windbgstub-utils.h
> @@ -62,6 +62,11 @@
>      _t;                                                       \
>  })
>
> +typedef struct InitedAddr {
> +    target_ulong addr;
> +    bool is_init;
> +} InitedAddr;
> +
>  bool windbg_on_load(void);
>  void windbg_on_exit(void);
>
> diff --git a/windbgstub-utils.c b/windbgstub-utils.c
> index b5fb6db3f2..662096647e 100755
> --- a/windbgstub-utils.c
> +++ b/windbgstub-utils.c
> @@ -11,10 +11,69 @@
>
>  #include "exec/windbgstub-utils.h"
>
> +#ifdef TARGET_X86_64
> +# define OFFSET_SELF_PCR         0x18
> +# define OFFSET_VERS             0x108
> +#else
> +# define OFFSET_SELF_PCR         0x1C
> +# define OFFSET_VERS             0x34
> +#endif
> +
> +typedef struct KDData {
> +    InitedAddr KPCR;
> +    InitedAddr version;
> +} KDData;
> +
> +static KDData *kd;
> +
>  bool windbg_on_load(void)
>  {
> -    return false;
> +    CPUState *cpu = qemu_get_cpu(0);
> +    CPUArchState *env = cpu->env_ptr;
> +
> +    if (!kd) {
> +        kd = g_new0(KDData, 1);
> +    }
> +
> +    if (!kd->KPCR.is_init) {
> +
> + #ifdef TARGET_X86_64
> +        kd->KPCR.addr = env->segs[R_GS].base;
> + #else
> +        kd->KPCR.addr = env->segs[R_FS].base;
> + #endif

What if Windows is rebooted and FS/GS changes? Do you need to flip
KPCR.is_init back to false on system reset?

> +        static target_ulong prev_KPCR;
> +        if (!kd->KPCR.addr || prev_KPCR == kd->KPCR.addr) {
> +            return false;
> +        }
> +        prev_KPCR = kd->KPCR.addr;
> +
> +        if (kd->KPCR.addr != READ_VMEM(cpu, kd->KPCR.addr + OFFSET_SELF_PCR,
> +                                       target_ulong)) {
> +            return false;
> +        }
> +
> +        kd->KPCR.is_init = true;
> +    }
> +
> +    if (!kd->version.is_init && kd->KPCR.is_init) {
> +        kd->version.addr = READ_VMEM(cpu, kd->KPCR.addr + OFFSET_VERS,
> +                                     target_ulong);
> +        if (!kd->version.addr) {
> +            return false;
> +        }
> +        kd->version.is_init = true;
> +    }
> +
> +    WINDBG_DEBUG("windbg_on_load: KPCR " FMT_ADDR, kd->KPCR.addr);
> +    WINDBG_DEBUG("windbg_on_load: version " FMT_ADDR, kd->version.addr);
> +
> +    return true;
>  }
>
>  void windbg_on_exit(void)
> -{}
> +{
> +    g_free(kd);
> +    kd = NULL;
> +}
>