[PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Ard Biesheuvel]

The EFI spec requires that on arm64 systems, all runtime code and data
regions that share a 64k page can be mapped with the same memory type
attributes. Unfortunately, this does not take permission attributes into
account, and so the firmware is permitted to expose runtime code and
data regions that share 64k pages, and this may prevent the OS from
using restricted permissions in such cases, e.g., map data regions with
non-exec attributes.

We currently emit a warning when hitting this at boot, but the warning
is problematic for a number of reasons:
- it uses WARN() which spews a lot of irrelevant information into the
  log about the execution context where the issue was detected;
- it only takes the start of the region into account and not the size

Let's just drop the warning, as the condition does not strictly violate
the spec (although it only occurs with U-Boot), and fix the check to
take both the start and the end addresses into account.

Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/kernel/efi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -25,8 +25,8 @@ static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
 	if (type == EFI_MEMORY_MAPPED_IO)
 		return PROT_DEVICE_nGnRE;
 
-	if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
-		      "UEFI Runtime regions are not aligned to 64 KB -- buggy firmware?"))
+	if (!PAGE_ALIGNED(md->phys_addr) ||
+	    !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
 		/*
 		 * If the region is not aligned to the page size of the OS, we
 		 * can not use strict permissions, since that would also affect
-- 
2.35.1


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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Heinrich Schuchardt]

On 11/5/22 23:52, Ard Biesheuvel wrote:
> The EFI spec requires that on arm64 systems, all runtime code and data
> regions that share a 64k page can be mapped with the same memory type
> attributes. Unfortunately, this does not take permission attributes into
> account, and so the firmware is permitted to expose runtime code and
> data regions that share 64k pages, and this may prevent the OS from
> using restricted permissions in such cases, e.g., map data regions with
> non-exec attributes.

This is the relevant paragraph in the UEFI specification:

<cite>
The ARM architecture allows mapping pages at a variety of granularities, 
including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB 
page with any of the following types listed below, then all 4KiB pages 
in the 64KiB page must use identical ARM Memory Page Attributes (as 
described in Map EFI Cacheability Attributes to AArch64 Memory Types):

- EfiRuntimeServicesCode
- EfiRuntimeServicesData
- EfiReserved
- EfiACPIMemoryNVS

Mixed attribute mappings within a larger page are not allowed.
</cite>

It remains unclear if only EFI Cacheability of also other page 
attributes are meant. The UEFI specification should be clarified in this 
respect.

> 
> We currently emit a warning when hitting this at boot, but the warning
> is problematic for a number of reasons:
> - it uses WARN() which spews a lot of irrelevant information into the
>    log about the execution context where the issue was detected;
> - it only takes the start of the region into account and not the size

Is the occurrence of the warning specific to U-Boot or do you see the 
warning with EDK II too?

> 
> Let's just drop the warning, as the condition does not strictly violate
> the spec (although it only occurs with U-Boot), and fix the check to
> take both the start and the end addresses into account.
> 
> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>   arch/arm64/kernel/efi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -25,8 +25,8 @@ static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
>   	if (type == EFI_MEMORY_MAPPED_IO)
>   		return PROT_DEVICE_nGnRE;
>   
> -	if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
> -		      "UEFI Runtime regions are not aligned to 64 KB -- buggy firmware?"))
> +	if (!PAGE_ALIGNED(md->phys_addr) ||
> +	    !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))

Enhancing the check is correct.

The warning tells that Linux cannot establish secure settings for some 
pages. It would be preferable to keep it and fix the UEFI specification 
and the firmware instead.

Best regards

Heinrich

>   		/*
>   		 * If the region is not aligned to the page size of the OS, we
>   		 * can not use strict permissions, since that would also affect

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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Heinrich Schuchardt]

On 11/6/22 00:24, Heinrich Schuchardt wrote:
> On 11/5/22 23:52, Ard Biesheuvel wrote:
>> The EFI spec requires that on arm64 systems, all runtime code and data
>> regions that share a 64k page can be mapped with the same memory type
>> attributes. Unfortunately, this does not take permission attributes into
>> account, and so the firmware is permitted to expose runtime code and
>> data regions that share 64k pages, and this may prevent the OS from
>> using restricted permissions in such cases, e.g., map data regions with
>> non-exec attributes.
> 
> This is the relevant paragraph in the UEFI specification:
> 
> <cite>
> The ARM architecture allows mapping pages at a variety of granularities, 
> including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB 
> page with any of the following types listed below, then all 4KiB pages 
> in the 64KiB page must use identical ARM Memory Page Attributes (as 
> described in Map EFI Cacheability Attributes to AArch64 Memory Types):
> 
> - EfiRuntimeServicesCode
> - EfiRuntimeServicesData
> - EfiReserved
> - EfiACPIMemoryNVS
> 
> Mixed attribute mappings within a larger page are not allowed.
> </cite>
> 
> It remains unclear if only EFI Cacheability of also other page 
> attributes are meant. The UEFI specification should be clarified in this 
> respect.
> 
>>
>> We currently emit a warning when hitting this at boot, but the warning
>> is problematic for a number of reasons:
>> - it uses WARN() which spews a lot of irrelevant information into the
>>    log about the execution context where the issue was detected;
>> - it only takes the start of the region into account and not the size
> 
> Is the occurrence of the warning specific to U-Boot or do you see the 
> warning with EDK II too?
> 
>>
>> Let's just drop the warning, as the condition does not strictly violate
>> the spec (although it only occurs with U-Boot), and fix the check to
>> take both the start and the end addresses into account.
>>
>> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
>> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>> ---
>>   arch/arm64/kernel/efi.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
>> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
>> --- a/arch/arm64/kernel/efi.c
>> +++ b/arch/arm64/kernel/efi.c
>> @@ -25,8 +25,8 @@ static __init pteval_t 
>> create_mapping_protection(efi_memory_desc_t *md)
>>       if (type == EFI_MEMORY_MAPPED_IO)
>>           return PROT_DEVICE_nGnRE;
>> -    if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
>> -              "UEFI Runtime regions are not aligned to 64 KB -- buggy 
>> firmware?"))
>> +    if (!PAGE_ALIGNED(md->phys_addr) ||
>> +        !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
> 
> Enhancing the check is correct.

The UEFI requirement is that within a 64 KiB page all memory descriptors
shall use the same page attributes if any 4 KiB sub-page is of one of 
the following types.

- EfiRuntimeServicesCode
- EfiRuntimeServicesData
- EfiReserved
- EfiACPIMemoryNVS

It is not required that memory descriptors shall be aligned to 64 KiB 
boundaries.

So the following map should not pose any problem:

00000-00fff - EfiBootServicesData (not used at runtime)
01000-13fff - EfiRuntimeServicesData
14000-1ffff - EfiRuntimeServicesData
20000-24fff - EfiRuntimeServicesCode
25000-27fff - EfiBootServicesCode (not used at runtime)
28000-3ffff - EfiRuntimeServicesCode

Evaluating each memory descriptor individually looks wrong. You first 
have to extend each memory descriptor of one of the four aforementioned 
memory types to the next 64 KiB boundary or within a 64 KiB boundary to 
the next descriptor of one of the aforementioned memory types. Next you 
have to merge adjacent descriptors with same attributes within the same 
64 KiB page.

So the map for which you set attributes would become

00000-1ffff - EfiRuntimeServicesData
20000-3ffff - EfiRuntimeServicesCode

I guess all that alignment and merging should go into efi_virtmap_init().

Best regards

Heinrich

> 
> The warning tells that Linux cannot establish secure settings for some 
> pages. It would be preferable to keep it and fix the UEFI specification 
> and the firmware instead.
> 
> Best regards
> 
> Heinrich
> 
>>           /*
>>            * If the region is not aligned to the page size of the OS, we
>>            * can not use strict permissions, since that would also affect

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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Ard Biesheuvel]

On Sun, 6 Nov 2022 at 03:27, Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
>
>
> On 11/6/22 00:24, Heinrich Schuchardt wrote:
> > On 11/5/22 23:52, Ard Biesheuvel wrote:
> >> The EFI spec requires that on arm64 systems, all runtime code and data
> >> regions that share a 64k page can be mapped with the same memory type
> >> attributes. Unfortunately, this does not take permission attributes into
> >> account, and so the firmware is permitted to expose runtime code and
> >> data regions that share 64k pages, and this may prevent the OS from
> >> using restricted permissions in such cases, e.g., map data regions with
> >> non-exec attributes.
> >
> > This is the relevant paragraph in the UEFI specification:
> >
> > <cite>
> > The ARM architecture allows mapping pages at a variety of granularities,
> > including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB
> > page with any of the following types listed below, then all 4KiB pages
> > in the 64KiB page must use identical ARM Memory Page Attributes (as
> > described in Map EFI Cacheability Attributes to AArch64 Memory Types):
> >
> > - EfiRuntimeServicesCode
> > - EfiRuntimeServicesData
> > - EfiReserved
> > - EfiACPIMemoryNVS
> >
> > Mixed attribute mappings within a larger page are not allowed.
> > </cite>
> >
> > It remains unclear if only EFI Cacheability of also other page
> > attributes are meant. The UEFI specification should be clarified in this
> > respect.
> >
> >>
> >> We currently emit a warning when hitting this at boot, but the warning
> >> is problematic for a number of reasons:
> >> - it uses WARN() which spews a lot of irrelevant information into the
> >>    log about the execution context where the issue was detected;
> >> - it only takes the start of the region into account and not the size
> >
> > Is the occurrence of the warning specific to U-Boot or do you see the
> > warning with EDK II too?
> >
> >>
> >> Let's just drop the warning, as the condition does not strictly violate
> >> the spec (although it only occurs with U-Boot), and fix the check to
> >> take both the start and the end addresses into account.
> >>
> >> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> >> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> >> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> >> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >> ---
> >>   arch/arm64/kernel/efi.c | 4 ++--
> >>   1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> >> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
> >> --- a/arch/arm64/kernel/efi.c
> >> +++ b/arch/arm64/kernel/efi.c
> >> @@ -25,8 +25,8 @@ static __init pteval_t
> >> create_mapping_protection(efi_memory_desc_t *md)
> >>       if (type == EFI_MEMORY_MAPPED_IO)
> >>           return PROT_DEVICE_nGnRE;
> >> -    if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
> >> -              "UEFI Runtime regions are not aligned to 64 KB -- buggy
> >> firmware?"))
> >> +    if (!PAGE_ALIGNED(md->phys_addr) ||
> >> +        !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
> >
> > Enhancing the check is correct.
>
> The UEFI requirement is that within a 64 KiB page all memory descriptors
> shall use the same page attributes if any 4 KiB sub-page is of one of
> the following types.
>
> - EfiRuntimeServicesCode
> - EfiRuntimeServicesData
> - EfiReserved
> - EfiACPIMemoryNVS
>
> It is not required that memory descriptors shall be aligned to 64 KiB
> boundaries.
>

Indeed, this is what I misremembered.

> So the following map should not pose any problem:
>
> 00000-00fff - EfiBootServicesData (not used at runtime)
> 01000-13fff - EfiRuntimeServicesData
> 14000-1ffff - EfiRuntimeServicesData
> 20000-24fff - EfiRuntimeServicesCode
> 25000-27fff - EfiBootServicesCode (not used at runtime)
> 28000-3ffff - EfiRuntimeServicesCode
>
> Evaluating each memory descriptor individually looks wrong. You first
> have to extend each memory descriptor of one of the four aforementioned
> memory types to the next 64 KiB boundary or within a 64 KiB boundary to
> the next descriptor of one of the aforementioned memory types. Next you
> have to merge adjacent descriptors with same attributes within the same
> 64 KiB page.
>

So now we have to look at adjacent descriptors, which means we have to
sort the memory map, as there is no guarantee that the descriptors
appear in order.

> So the map for which you set attributes would become
>
> 00000-1ffff - EfiRuntimeServicesData
> 20000-3ffff - EfiRuntimeServicesCode
>
> I guess all that alignment and merging should go into efi_virtmap_init().
>

U-boot does not provide a memory attributes table either, so we don't
know which parts of the code regions should be mapped R-X and which
parts RW- (Firmware implementations such as EDK2 that are based on
PE/COFF images internally use code descriptors for each executable,
which means they cover both the .text/.rodata and .data/.bss sections
of the image. The data descriptors are used for dynamic allocations).

This is why we use RWX for RTcode and RW- for RTdata in absence of the
RO/XP attributes (which are passed via the memory attributes table
usually).

So in summary, I think the patch is fine. The warning is spurious
given that the condition in question is actually permitted by the
spec.

On the uboot side, which already seems to align and round up RTcode
sections to 64k, we might set the EFI_MEMORY_RO attribute on such
regions if they really only contain .text and .rodata segments, and
can tolerate being mapped without writable permissions. That way, the
kernel will understand that it does not need to provide RWX
permissions, which is really what all this code is trying to prevent.

Thanks,
Ard.

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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Ard Biesheuvel]

On Sun, 6 Nov 2022 at 10:48, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Sun, 6 Nov 2022 at 03:27, Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
> >
> >
> >
> > On 11/6/22 00:24, Heinrich Schuchardt wrote:
> > > On 11/5/22 23:52, Ard Biesheuvel wrote:
> > >> The EFI spec requires that on arm64 systems, all runtime code and data
> > >> regions that share a 64k page can be mapped with the same memory type
> > >> attributes. Unfortunately, this does not take permission attributes into
> > >> account, and so the firmware is permitted to expose runtime code and
> > >> data regions that share 64k pages, and this may prevent the OS from
> > >> using restricted permissions in such cases, e.g., map data regions with
> > >> non-exec attributes.
> > >
> > > This is the relevant paragraph in the UEFI specification:
> > >
> > > <cite>
> > > The ARM architecture allows mapping pages at a variety of granularities,
> > > including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB
> > > page with any of the following types listed below, then all 4KiB pages
> > > in the 64KiB page must use identical ARM Memory Page Attributes (as
> > > described in Map EFI Cacheability Attributes to AArch64 Memory Types):
> > >
> > > - EfiRuntimeServicesCode
> > > - EfiRuntimeServicesData
> > > - EfiReserved
> > > - EfiACPIMemoryNVS
> > >
> > > Mixed attribute mappings within a larger page are not allowed.
> > > </cite>
> > >
> > > It remains unclear if only EFI Cacheability of also other page
> > > attributes are meant. The UEFI specification should be clarified in this
> > > respect.
> > >
> > >>
> > >> We currently emit a warning when hitting this at boot, but the warning
> > >> is problematic for a number of reasons:
> > >> - it uses WARN() which spews a lot of irrelevant information into the
> > >>    log about the execution context where the issue was detected;
> > >> - it only takes the start of the region into account and not the size
> > >
> > > Is the occurrence of the warning specific to U-Boot or do you see the
> > > warning with EDK II too?
> > >
> > >>
> > >> Let's just drop the warning, as the condition does not strictly violate
> > >> the spec (although it only occurs with U-Boot), and fix the check to
> > >> take both the start and the end addresses into account.
> > >>
> > >> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> > >> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > >> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> > >> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > >> ---
> > >>   arch/arm64/kernel/efi.c | 4 ++--
> > >>   1 file changed, 2 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> > >> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
> > >> --- a/arch/arm64/kernel/efi.c
> > >> +++ b/arch/arm64/kernel/efi.c
> > >> @@ -25,8 +25,8 @@ static __init pteval_t
> > >> create_mapping_protection(efi_memory_desc_t *md)
> > >>       if (type == EFI_MEMORY_MAPPED_IO)
> > >>           return PROT_DEVICE_nGnRE;
> > >> -    if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
> > >> -              "UEFI Runtime regions are not aligned to 64 KB -- buggy
> > >> firmware?"))
> > >> +    if (!PAGE_ALIGNED(md->phys_addr) ||
> > >> +        !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
> > >
> > > Enhancing the check is correct.
> >
> > The UEFI requirement is that within a 64 KiB page all memory descriptors
> > shall use the same page attributes if any 4 KiB sub-page is of one of
> > the following types.
> >
> > - EfiRuntimeServicesCode
> > - EfiRuntimeServicesData
> > - EfiReserved
> > - EfiACPIMemoryNVS
> >
> > It is not required that memory descriptors shall be aligned to 64 KiB
> > boundaries.
> >
>
> Indeed, this is what I misremembered.
>
> > So the following map should not pose any problem:
> >
> > 00000-00fff - EfiBootServicesData (not used at runtime)
> > 01000-13fff - EfiRuntimeServicesData
> > 14000-1ffff - EfiRuntimeServicesData
> > 20000-24fff - EfiRuntimeServicesCode
> > 25000-27fff - EfiBootServicesCode (not used at runtime)
> > 28000-3ffff - EfiRuntimeServicesCode
> >
> > Evaluating each memory descriptor individually looks wrong. You first
> > have to extend each memory descriptor of one of the four aforementioned
> > memory types to the next 64 KiB boundary or within a 64 KiB boundary to
> > the next descriptor of one of the aforementioned memory types. Next you
> > have to merge adjacent descriptors with same attributes within the same
> > 64 KiB page.
> >
>
> So now we have to look at adjacent descriptors, which means we have to
> sort the memory map, as there is no guarantee that the descriptors
> appear in order.
>
> > So the map for which you set attributes would become
> >
> > 00000-1ffff - EfiRuntimeServicesData
> > 20000-3ffff - EfiRuntimeServicesCode
> >
> > I guess all that alignment and merging should go into efi_virtmap_init().
> >
>
> U-boot does not provide a memory attributes table either, so we don't
> know which parts of the code regions should be mapped R-X and which
> parts RW- (Firmware implementations such as EDK2 that are based on
> PE/COFF images internally use code descriptors for each executable,
> which means they cover both the .text/.rodata and .data/.bss sections
> of the image. The data descriptors are used for dynamic allocations).
>
> This is why we use RWX for RTcode and RW- for RTdata in absence of the
> RO/XP attributes (which are passed via the memory attributes table
> usually).
>
> So in summary, I think the patch is fine. The warning is spurious
> given that the condition in question is actually permitted by the
> spec.
>
> On the uboot side, which already seems to align and round up RTcode
> sections to 64k, we might set the EFI_MEMORY_RO attribute on such
> regions if they really only contain .text and .rodata segments, and
> can tolerate being mapped without writable permissions. That way, the
> kernel will understand that it does not need to provide RWX
> permissions, which is really what all this code is trying to prevent.
>

OK, this is not entirely true. Setting EFI_MEMORY_RO on sufficiently
aligned RTcode descriptors that don't require read-write permissions
would definitely be an improvement, but the current code would still
use RWX for RTdata sections that are not aligned to 64k (on 16k or 64k
pagesize OS builds) because otherwise, we'd have to go over the EFI
memory map again to check whether setting RW- on the RTdata region in
question would not result in an adjacent RTcode region losing its
executable permissions.

So what we might do is detect this condition, and if it triggers, go
over the memory map again and map all misaligned RTcode descriptors
again. I'll go and code this up and send a v2.

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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Heinrich Schuchardt]

On 11/6/22 10:48, Ard Biesheuvel wrote:
> On Sun, 6 Nov 2022 at 03:27, Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
>>
>>
>>
>> On 11/6/22 00:24, Heinrich Schuchardt wrote:
>>> On 11/5/22 23:52, Ard Biesheuvel wrote:
>>>> The EFI spec requires that on arm64 systems, all runtime code and data
>>>> regions that share a 64k page can be mapped with the same memory type
>>>> attributes. Unfortunately, this does not take permission attributes into
>>>> account, and so the firmware is permitted to expose runtime code and
>>>> data regions that share 64k pages, and this may prevent the OS from
>>>> using restricted permissions in such cases, e.g., map data regions with
>>>> non-exec attributes.
>>>
>>> This is the relevant paragraph in the UEFI specification:
>>>
>>> <cite>
>>> The ARM architecture allows mapping pages at a variety of granularities,
>>> including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB
>>> page with any of the following types listed below, then all 4KiB pages
>>> in the 64KiB page must use identical ARM Memory Page Attributes (as
>>> described in Map EFI Cacheability Attributes to AArch64 Memory Types):
>>>
>>> - EfiRuntimeServicesCode
>>> - EfiRuntimeServicesData
>>> - EfiReserved
>>> - EfiACPIMemoryNVS
>>>
>>> Mixed attribute mappings within a larger page are not allowed.
>>> </cite>
>>>
>>> It remains unclear if only EFI Cacheability of also other page
>>> attributes are meant. The UEFI specification should be clarified in this
>>> respect.
>>>
>>>>
>>>> We currently emit a warning when hitting this at boot, but the warning
>>>> is problematic for a number of reasons:
>>>> - it uses WARN() which spews a lot of irrelevant information into the
>>>>     log about the execution context where the issue was detected;
>>>> - it only takes the start of the region into account and not the size
>>>
>>> Is the occurrence of the warning specific to U-Boot or do you see the
>>> warning with EDK II too?
>>>
>>>>
>>>> Let's just drop the warning, as the condition does not strictly violate
>>>> the spec (although it only occurs with U-Boot), and fix the check to
>>>> take both the start and the end addresses into account.
>>>>
>>>> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
>>>> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>>>> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>> ---
>>>>    arch/arm64/kernel/efi.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
>>>> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
>>>> --- a/arch/arm64/kernel/efi.c
>>>> +++ b/arch/arm64/kernel/efi.c
>>>> @@ -25,8 +25,8 @@ static __init pteval_t
>>>> create_mapping_protection(efi_memory_desc_t *md)
>>>>        if (type == EFI_MEMORY_MAPPED_IO)
>>>>            return PROT_DEVICE_nGnRE;
>>>> -    if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
>>>> -              "UEFI Runtime regions are not aligned to 64 KB -- buggy
>>>> firmware?"))
>>>> +    if (!PAGE_ALIGNED(md->phys_addr) ||
>>>> +        !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
>>>
>>> Enhancing the check is correct.
>>
>> The UEFI requirement is that within a 64 KiB page all memory descriptors
>> shall use the same page attributes if any 4 KiB sub-page is of one of
>> the following types.
>>
>> - EfiRuntimeServicesCode
>> - EfiRuntimeServicesData
>> - EfiReserved
>> - EfiACPIMemoryNVS
>>
>> It is not required that memory descriptors shall be aligned to 64 KiB
>> boundaries.
>>
> 
> Indeed, this is what I misremembered.
> 
>> So the following map should not pose any problem:
>>
>> 00000-00fff - EfiBootServicesData (not used at runtime)
>> 01000-13fff - EfiRuntimeServicesData
>> 14000-1ffff - EfiRuntimeServicesData
>> 20000-24fff - EfiRuntimeServicesCode
>> 25000-27fff - EfiBootServicesCode (not used at runtime)
>> 28000-3ffff - EfiRuntimeServicesCode
>>
>> Evaluating each memory descriptor individually looks wrong. You first
>> have to extend each memory descriptor of one of the four aforementioned
>> memory types to the next 64 KiB boundary or within a 64 KiB boundary to
>> the next descriptor of one of the aforementioned memory types. Next you
>> have to merge adjacent descriptors with same attributes within the same
>> 64 KiB page.
>>
> 
> So now we have to look at adjacent descriptors, which means we have to
> sort the memory map, as there is no guarantee that the descriptors
> appear in order.
> 
>> So the map for which you set attributes would become
>>
>> 00000-1ffff - EfiRuntimeServicesData
>> 20000-3ffff - EfiRuntimeServicesCode
>>
>> I guess all that alignment and merging should go into efi_virtmap_init().
>>
> 
> U-boot does not provide a memory attributes table either, so we don't
> know which parts of the code regions should be mapped R-X and which
> parts RW- (Firmware implementations such as EDK2 that are based on
> PE/COFF images internally use code descriptors for each executable,
> which means they cover both the .text/.rodata and .data/.bss sections
> of the image. The data descriptors are used for dynamic allocations).
> 
> This is why we use RWX for RTcode and RW- for RTdata in absence of the
> RO/XP attributes (which are passed via the memory attributes table
> usually).
> 
> So in summary, I think the patch is fine. The warning is spurious
> given that the condition in question is actually permitted by the
> spec.
> 
> On the uboot side, which already seems to align and round up RTcode
> sections to 64k, we might set the EFI_MEMORY_RO attribute on such
> regions if they really only contain .text and .rodata segments, and
> can tolerate being mapped without writable permissions. That way, the
> kernel will understand that it does not need to provide RWX
> permissions, which is really what all this code is trying to prevent.

Shouldn't EFI_MEMORY_RO only be set if the UEFI firmware actually sets 
up the MMU to make the corresponding memory read only?

Best regards

Heinrich

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Re: [PATCH] arm64: efi: Make runtime region misalignment warning less noisy

[Ard Biesheuvel]

On Sun, 6 Nov 2022 at 11:44, Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
>
>
> On 11/6/22 10:48, Ard Biesheuvel wrote:
> > On Sun, 6 Nov 2022 at 03:27, Heinrich Schuchardt
> > <heinrich.schuchardt@canonical.com> wrote:
> >>
> >>
> >>
> >> On 11/6/22 00:24, Heinrich Schuchardt wrote:
> >>> On 11/5/22 23:52, Ard Biesheuvel wrote:
> >>>> The EFI spec requires that on arm64 systems, all runtime code and data
> >>>> regions that share a 64k page can be mapped with the same memory type
> >>>> attributes. Unfortunately, this does not take permission attributes into
> >>>> account, and so the firmware is permitted to expose runtime code and
> >>>> data regions that share 64k pages, and this may prevent the OS from
> >>>> using restricted permissions in such cases, e.g., map data regions with
> >>>> non-exec attributes.
> >>>
> >>> This is the relevant paragraph in the UEFI specification:
> >>>
> >>> <cite>
> >>> The ARM architecture allows mapping pages at a variety of granularities,
> >>> including 4KiB and 64KiB. If a 64KiB physical page contains any 4KiB
> >>> page with any of the following types listed below, then all 4KiB pages
> >>> in the 64KiB page must use identical ARM Memory Page Attributes (as
> >>> described in Map EFI Cacheability Attributes to AArch64 Memory Types):
> >>>
> >>> - EfiRuntimeServicesCode
> >>> - EfiRuntimeServicesData
> >>> - EfiReserved
> >>> - EfiACPIMemoryNVS
> >>>
> >>> Mixed attribute mappings within a larger page are not allowed.
> >>> </cite>
> >>>
> >>> It remains unclear if only EFI Cacheability of also other page
> >>> attributes are meant. The UEFI specification should be clarified in this
> >>> respect.
> >>>
> >>>>
> >>>> We currently emit a warning when hitting this at boot, but the warning
> >>>> is problematic for a number of reasons:
> >>>> - it uses WARN() which spews a lot of irrelevant information into the
> >>>>     log about the execution context where the issue was detected;
> >>>> - it only takes the start of the region into account and not the size
> >>>
> >>> Is the occurrence of the warning specific to U-Boot or do you see the
> >>> warning with EDK II too?
> >>>
> >>>>
> >>>> Let's just drop the warning, as the condition does not strictly violate
> >>>> the spec (although it only occurs with U-Boot), and fix the check to
> >>>> take both the start and the end addresses into account.
> >>>>
> >>>> Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> >>>> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> >>>> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> >>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >>>> ---
> >>>>    arch/arm64/kernel/efi.c | 4 ++--
> >>>>    1 file changed, 2 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> >>>> index e1be6c429810d0d5..3dd6f0c66f8aeb78 100644
> >>>> --- a/arch/arm64/kernel/efi.c
> >>>> +++ b/arch/arm64/kernel/efi.c
> >>>> @@ -25,8 +25,8 @@ static __init pteval_t
> >>>> create_mapping_protection(efi_memory_desc_t *md)
> >>>>        if (type == EFI_MEMORY_MAPPED_IO)
> >>>>            return PROT_DEVICE_nGnRE;
> >>>> -    if (WARN_ONCE(!PAGE_ALIGNED(md->phys_addr),
> >>>> -              "UEFI Runtime regions are not aligned to 64 KB -- buggy
> >>>> firmware?"))
> >>>> +    if (!PAGE_ALIGNED(md->phys_addr) ||
> >>>> +        !PAGE_ALIGNED(md->num_pages * EFI_PAGE_SIZE))
> >>>
> >>> Enhancing the check is correct.
> >>
> >> The UEFI requirement is that within a 64 KiB page all memory descriptors
> >> shall use the same page attributes if any 4 KiB sub-page is of one of
> >> the following types.
> >>
> >> - EfiRuntimeServicesCode
> >> - EfiRuntimeServicesData
> >> - EfiReserved
> >> - EfiACPIMemoryNVS
> >>
> >> It is not required that memory descriptors shall be aligned to 64 KiB
> >> boundaries.
> >>
> >
> > Indeed, this is what I misremembered.
> >
> >> So the following map should not pose any problem:
> >>
> >> 00000-00fff - EfiBootServicesData (not used at runtime)
> >> 01000-13fff - EfiRuntimeServicesData
> >> 14000-1ffff - EfiRuntimeServicesData
> >> 20000-24fff - EfiRuntimeServicesCode
> >> 25000-27fff - EfiBootServicesCode (not used at runtime)
> >> 28000-3ffff - EfiRuntimeServicesCode
> >>
> >> Evaluating each memory descriptor individually looks wrong. You first
> >> have to extend each memory descriptor of one of the four aforementioned
> >> memory types to the next 64 KiB boundary or within a 64 KiB boundary to
> >> the next descriptor of one of the aforementioned memory types. Next you
> >> have to merge adjacent descriptors with same attributes within the same
> >> 64 KiB page.
> >>
> >
> > So now we have to look at adjacent descriptors, which means we have to
> > sort the memory map, as there is no guarantee that the descriptors
> > appear in order.
> >
> >> So the map for which you set attributes would become
> >>
> >> 00000-1ffff - EfiRuntimeServicesData
> >> 20000-3ffff - EfiRuntimeServicesCode
> >>
> >> I guess all that alignment and merging should go into efi_virtmap_init().
> >>
> >
> > U-boot does not provide a memory attributes table either, so we don't
> > know which parts of the code regions should be mapped R-X and which
> > parts RW- (Firmware implementations such as EDK2 that are based on
> > PE/COFF images internally use code descriptors for each executable,
> > which means they cover both the .text/.rodata and .data/.bss sections
> > of the image. The data descriptors are used for dynamic allocations).
> >
> > This is why we use RWX for RTcode and RW- for RTdata in absence of the
> > RO/XP attributes (which are passed via the memory attributes table
> > usually).
> >
> > So in summary, I think the patch is fine. The warning is spurious
> > given that the condition in question is actually permitted by the
> > spec.
> >
> > On the uboot side, which already seems to align and round up RTcode
> > sections to 64k, we might set the EFI_MEMORY_RO attribute on such
> > regions if they really only contain .text and .rodata segments, and
> > can tolerate being mapped without writable permissions. That way, the
> > kernel will understand that it does not need to provide RWX
> > permissions, which is really what all this code is trying to prevent.
>
> Shouldn't EFI_MEMORY_RO only be set if the UEFI firmware actually sets
> up the MMU to make the corresponding memory read only?
>

No. The EFI_MEMORY_RO and XP attributes describe the nature of the
contents of the regions, i.e., if they support being mapped with
read-only resp. non-executable permissions. The same applies to the
memory type attributes, btw: on bare metal, the memory is usually
described as WC|WT|WB and it is up to the OS to choose between memory
types when it creates the mapping - how the firmware maps it is
irrelevant.

In general, the OS does not care or even tries to determine how the
firmware has programmed the MMU and the page tables.

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