Re: [edk2-devel] [Patch V4 04/15] MdeModulePkg: Remove RO and NX protection when unset guard page

["duntan" <dun.tan@intel.com>]

Hi Kun,

When we unset a guarded page to unguarded, from page table perspective, it's to set a non-present page to present.
I think it's reasonable that we should specific memory attribute to appropriate value when map non-present range to present. In smm initial page table, free page is set to present, writable and executable(with Present bit(bit0) and R/W bit(bit1) set to 1, XD(bit 63) set to 0). So that's why I also clear xp.

Thanks,
Dun

-----Original Message-----
From: Kun Qin <kuqin12@gmail.com> 
Sent: Wednesday, May 17, 2023 3:05 AM
To: devel@edk2.groups.io; Tan, Dun <dun.tan@intel.com>
Cc: Gao, Liming <gaoliming@byosoft.com.cn>; Ni, Ray <ray.ni@intel.com>; Wang, Jian J <jian.j.wang@intel.com>
Subject: Re: [edk2-devel] [Patch V4 04/15] MdeModulePkg: Remove RO and NX protection when unset guard page

Hi Dun,

I might have missed the context, but could you please explain why we need to clear "EFI_MEMORY_XP"?

It is understandable that you would like to clear RO. But would it make more sense to clear XP only when needed (i.e. code page allocation)?

Thanks,
Kun

On 5/16/2023 2:59 AM, duntan wrote:
> Remove RO and NX protection when unset guard page.
> When UnsetGuardPage(), remove all the memory attribute protection for 
> guarded page.
>
> Signed-off-by: Dun Tan <dun.tan@intel.com>
> Cc: Liming Gao <gaoliming@byosoft.com.cn>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> ---
>   MdeModulePkg/Core/PiSmmCore/HeapGuard.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/MdeModulePkg/Core/PiSmmCore/HeapGuard.c 
> b/MdeModulePkg/Core/PiSmmCore/HeapGuard.c
> index 8f3bab6fee..7daeeccf13 100644
> --- a/MdeModulePkg/Core/PiSmmCore/HeapGuard.c
> +++ b/MdeModulePkg/Core/PiSmmCore/HeapGuard.c
> @@ -553,7 +553,7 @@ UnsetGuardPage (
>                                            mSmmMemoryAttribute,
>                                            BaseAddress,
>                                            EFI_PAGE_SIZE,
> -                                         EFI_MEMORY_RP
> +                                         
> + EFI_MEMORY_RP|EFI_MEMORY_RO|EFI_MEMORY_XP
>                                            );
>       ASSERT_EFI_ERROR (Status);
>       mOnGuarding = FALSE;