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use RT_PROPERTIES table to implement efi=novamap

PATCH Applied Ard Biesheuvel 3 participants 6 messages Mar 5, 2021 – May 26, 2021

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Ard Biesheuvel

author maintainer
#0 lore raw

cover use RT_PROPERTIES table to implement efi=novamap

This patch addresses an oversight on my part when I implemented Linux side support for the EFI RT properties table: SetVirtualAddressMap() is itself a runtime service which is only callable at runtime to begin with, and so the EFI stub should only call it if it is not marked as unsupported.

This may be useful for the Snapdragon EFI based laptops, which already rely on a special EFI driver to expose the correct DT based on metadata exposed by EFI. These systems ship with a broken implementation of SetVirtualAddressMap, which is currently being worked around by passing efi=novamap on the kernel. command line.

After applying this patch (which I intend to propose for backporting to 5.10), the same can be achieved by exposing a RT_PROP table that marks SetVAMap() as unsupported. And while at it, better mark the variable services as unsupported as well, since they don't work under Linux either.

I'm open to extending this with a Linux specific override value kept in a EFI variable, so that platforms that cannot support DtbLoader are able to implement something similar.

Cc Jeffrey Hugo <[email protected]>,
Cc Bjorn Andersson <[email protected]>
Cc Shawn Guo <[email protected]>
Cc Rob Clark <[email protected]>
Cc Leif Lindholm <[email protected]>
Cc [email protected]

Ard Biesheuvel (1):
efi: stub: omit SetVirtualAddressMap() if marked unsupported in
RT_PROP table

 drivers/firmware/efi/libstub/efi-stub.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
Signature · 1 line
2.30.1
author maintainer
#1 lore raw

PATCH 1/1 efi: stub: omit SetVirtualAddressMap() if marked unsupported in RT_PROP table

The EFI_RT_PROPERTIES_TABLE contains a mask of runtime services that are available after ExitBootServices(). This mostly does not concern the EFI stub at all, given that it runs before that. However, there is one call that is made at runtime, which is the call to SetVirtualAddressMap() (which is not even callable at boot time to begin with)

So add the missing handling of the RT_PROP table to ensure that we only call SetVirtualAddressMap() if it is not being advertised as unsupported by the firmware.

Signed-off-by Ard Biesheuvel <[email protected]>
---
 drivers/firmware/efi/libstub/efi-stub.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
drivers/firmware/efi/libstub/efi-stub.c +16 -0
index ec2f3985bef3..26e69788f27a 100644
@@ -96,6 +96,18 @@ static void install_memreserve_table(void)
 		efi_err("Failed to install memreserve config table!\n");
 }
 
+static u32 get_supported_rt_services(void)
+{
+	const efi_rt_properties_table_t *rt_prop_table;
+	u32 supported = EFI_RT_SUPPORTED_ALL;
+
+	rt_prop_table = get_efi_config_table(EFI_RT_PROPERTIES_TABLE_GUID);
+	if (rt_prop_table)
+		supported &= rt_prop_table->runtime_services_supported;
+
+	return supported;
+}
+
 /*
  * EFI entry point for the arm/arm64 EFI stubs.  This is the entrypoint
  * that is described in the PE/COFF header.  Most of the code is the same

@@ -250,6 +262,10 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 			  (prop_tbl->memory_protection_attribute &
 			   EFI_PROPERTIES_RUNTIME_MEMORY_PROTECTION_NON_EXECUTABLE_PE_DATA);
 
+	/* force efi_novamap if SetVirtualAddressMap() is unsupported */
+	efi_novamap |= !(get_supported_rt_services() &
+			 EFI_RT_SUPPORTED_SET_VIRTUAL_ADDRESS_MAP);
+
 	/* hibernation expects the runtime regions to stay in the same place */
 	if (!IS_ENABLED(CONFIG_HIBERNATION) && !efi_nokaslr && !flat_va_mapping) {
 		/*
Signature · 1 line
2.30.1
Tested-by on v1 1/1
#2 lore raw

Re: [PATCH 1/1] efi: stub: omit SetVirtualAddressMap() if marked unsupported in RT_PROP table

Quoted 11 lines · Ard Biesheuvel

The EFI_RT_PROPERTIES_TABLE contains a mask of runtime services that are available after ExitBootServices(). This mostly does not concern the EFI stub at all, given that it runs before that. However, there is one call that is made at runtime, which is the call to SetVirtualAddressMap() (which is not even callable at boot time to begin with)

So add the missing handling of the RT_PROP table to ensure that we only call SetVirtualAddressMap() if it is not being advertised as unsupported by the firmware.

Signed-off-by Ard Biesheuvel <[email protected]>

On Lenovo Yoga C630 laptop:

Tested-by Shawn Guo <[email protected]>

It's a great help to dropping 'efi=novamap' kernel cmdline, which is a very nice thing for distros to support Snapdragon laptops.

Thanks much, Ard!

Shawn

author maintainer
#3 lore raw
In reply to Ard Biesheuvel
Quoted 12 lines · Ard Biesheuvel

This patch addresses an oversight on my part when I implemented Linux side support for the EFI RT properties table: SetVirtualAddressMap() is itself a runtime service which is only callable at runtime to begin with, and so the EFI stub should only call it if it is not marked as unsupported.

This may be useful for the Snapdragon EFI based laptops, which already rely on a special EFI driver to expose the correct DT based on metadata exposed by EFI. These systems ship with a broken implementation of SetVirtualAddressMap, which is currently being worked around by passing efi=novamap on the kernel. command line.

Quoted 9 lines

After applying this patch (which I intend to propose for backporting to 5.10), the same can be achieved by exposing a RT_PROP table that marks SetVAMap() as unsupported. And while at it, better mark the variable services as unsupported as well, since they don't work under Linux either.

I'm open to extending this with a Linux specific override value kept in a EFI variable, so that platforms that cannot support DtbLoader are able to implement something similar.

... or perhaps even in a DT property that gets AND'ed with the supported RT services mask bu the EFI stub before it boots the kernel proper.

#4 lore raw
In reply to Ard Biesheuvel
Quoted 11 lines · Ard Biesheuvel

This patch addresses an oversight on my part when I implemented Linux side support for the EFI RT properties table: SetVirtualAddressMap() is itself a runtime service which is only callable at runtime to begin with, and so the EFI stub should only call it if it is not marked as unsupported.

This may be useful for the Snapdragon EFI based laptops, which already rely on a special EFI driver to expose the correct DT based on metadata exposed by EFI. These systems ship with a broken implementation of SetVirtualAddressMap, which is currently being worked around by passing efi=novamap on the kernel. command line.

Quoted 8 lines

After applying this patch (which I intend to propose for backporting to 5.10), the same can be achieved by exposing a RT_PROP table that marks SetVAMap() as unsupported. And while at it, better mark the variable services as unsupported as well, since they don't work under Linux either.

I'm open to extending this with a Linux specific override value kept in a EFI variable, so that platforms that cannot support DtbLoader are able to implement something similar.

Yes, that will be much appreciated! IMHO, this is definitely an useful addition, as DtbLoader shouldn't be mandated. In some cases, people may choose to load DTB with other means, or DTB is not required at all. Yeah, ACPI kernel is already useful for these laptops, not only for running installer but also as a console based native arm64 machine.

Looking forward to something for testing :)

Shawn

CI Applied
#5 lore raw
In reply to Ard Biesheuvel
This patch was applied to qcom/linux.git (refs/heads/for-next):

Hello:

This patch was applied to qcom/linux.git (refs/heads/for-next):

Quoted 5 lines · On Fri, 5 Mar 2021 10:39:57 +0100 you wrote:

This patch addresses an oversight on my part when I implemented Linux side support for the EFI RT properties table: SetVirtualAddressMap() is itself a runtime service which is only callable at runtime to begin with, and so the EFI stub should only call it if it is not marked as unsupported.

Quoted 7 lines

This may be useful for the Snapdragon EFI based laptops, which already rely on a special EFI driver to expose the correct DT based on metadata exposed by EFI. These systems ship with a broken implementation of SetVirtualAddressMap, which is currently being worked around by passing efi=novamap on the kernel. command line.

[...]

Here is the summary with links:
- [1/1] efi: stub: omit SetVirtualAddressMap() if marked unsupported in RT_PROP table

    https://git.kernel.org/qcom/c/9e9888a0fe97

You are awesome, thank you!
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