linux-kernel - Re: [PATCH 1/2] ARM/efi: Remove duplicate permission settings

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Message-ID: <BD93A8DBE27154B0+22bf4a83-a850-4f78-8e0d-84cc93fe2715@uniontech.com>
Date: Thu, 30 Oct 2025 15:36:16 +0800
From: Qiang Ma <maqianga@...ontech.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: linux@...linux.org.uk, linux-efi@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] ARM/efi: Remove duplicate permission settings


在 2025/10/29 22:15, Ard Biesheuvel 写道:
> On Wed, 29 Oct 2025 at 10:55, Qiang Ma <maqianga@...ontech.com> wrote:
>>
>> 在 2025/10/28 21:42, Ard Biesheuvel 写道:
>>> On Mon, 27 Oct 2025 at 04:46, Qiang Ma <maqianga@...ontech.com> wrote:
>>>> 在 2025/10/23 16:30, Ard Biesheuvel 写道:
>>>>> On Thu, 23 Oct 2025 at 10:22, Qiang Ma <maqianga@...ontech.com> wrote:
>>>>>> In the efi_virtmap_init(), permission settings have been applied:
>>>>>>
>>>>>> static bool __init efi_virtmap_init(void)
>>>>>> {
>>>>>>            ...
>>>>>>            for_each_efi_memory_desc(md)
>>>>>>                    ...
>>>>>>                    efi_create_mapping(&efi_mm, md);
>>>>>>            ...
>>>>>>            efi_memattr_apply_permissions(&efi_mm, efi_set_mapping_permissions);
>>>>>>            ...
>>>>>> }
>>>>>>
>>>>>> Therefore, there is no need to apply it again in the efi_create_mapping().
>>>>>>
>>>>>> Fixes: 9fc68b717c24 ("ARM/efi: Apply strict permissions for UEFI Runtime Services regions")
>>>>>>
>>>>>> Signed-off-by: Qiang Ma <maqianga@...ontech.com>
>>>>> No, efi_memattr_apply_permissions() uses the /optional/ memory
>>>>> attributes table, whereas efi_create_mapping() uses the permission
>>>>> attributes in the EFI memory map. The memory attributes table is
>>>>> optional, in which case any RO/XP attributes from the memory map
>>>>> should be used.
>>>>>
>>>> I see.
>>>>
>>>> Then, can it be modified like this?
>>> No
>>>
>>>> --- a/arch/arm/kernel/efi.c
>>>> +++ b/arch/arm/kernel/efi.c
>>>> @@ -65,16 +65,13 @@ int __init efi_create_mapping(struct mm_struct *mm,
>>>> efi_memory_desc_t *md)
>>>>                    desc.type = MT_MEMORY_RWX_NONCACHED;
>>>>            else if (md->attribute & EFI_MEMORY_WC)
>>>>                    desc.type = MT_DEVICE_WC;
>>>> +       else if (md->attribute & (EFI_MEMORY_RO | EFI_MEMORY_XP))
>>> This will be true for RO, XP or RO+XP.
>>>
>>>> +               desc.type = MT_MEMORY_RO;
>>> This will apply RO permissions even to XP regions, which need to be writable.
>>>
>> Thanks for your review.
>> I see.
>>
>> I can introduce a new type MT_MEMORY_RO_XP, to describe RO+XP,
>> and then we can use the RO+XP attribute to implement memory mapping.
>>
> Why? The current code is working fine, no?
>
Yes, the current code is running normally.

The reasons for the modification are as follows:
I noticed that the arm64/RISC-V efi_create_mapping() always return 0,
but in the code where efi_virtmap_init() calls it, it is as follows:

ret = efi_create_mapping(&efi_mm, md);
if (ret) {
     pr_warn("  EFI remap %pa: failed to create mapping (%d)\n",
         &phys, ret);
     return false;
}

This return error print is unnecessary, so I want to remove it.
But, the return value of efi_create_mapping() in the arm doesn't
always return 0, so I'm trying to modify it.