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

[Qiang Ma]

在 2025/10/28 21:42, Ard Biesheuvel 写道:
> On Mon, 27 Oct 2025 at 04:46, Qiang Ma <maqianga@xxxxxxxxxxxxx> wrote:
> > 在 2025/10/23 16:30, Ard Biesheuvel 写道:
> > > On Thu, 23 Oct 2025 at 10:22, Qiang Ma <maqianga@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > 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.

--- a/arch/arm/kernel/efi.c
+++ b/arch/arm/kernel/efi.c
@@ -68,13 +68,16 @@ int __init efi_create_mapping(struct mm_struct *mm, 
efi_memory_desc_t *md)
        else
                desc.type = MT_DEVICE;

+       if ((md->attribute & EFI_MEMORY_RO) &&
+           (md->attribute & EFI_MEMORY_XP))
+               desc.type = MT_MEMORY_RO_XP;
+       else if ((md->attribute & EFI_MEMORY_RO)
+               desc.type = MT_MEMORY_RO;
+       else if (md->attribute & EFI_MEMORY_XP)
+               desc.type = MT_MEMORY_RW;
+
        create_mapping_late(mm, &desc, true);