linux-kernel - [PATCH] x86/efi: Don't unmap EFI boot services code/data regions for EFI_OLD_MEMMAP and EFI_MIXED

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Date:   Fri, 21 Dec 2018 18:22:34 -0800
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH] x86/efi: Don't unmap EFI boot services code/data regions for EFI_OLD_MEMMAP and EFI_MIXED_MODE

Commit d5052a7130a6 ("x86/efi: Unmap EFI boot services code/data regions
from efi_pgd") forgets to take two EFI modes into consideration namely
EFI_OLD_MEMMAP and EFI_MIXED_MODE.

EFI_OLD_MEMMAP is a legacy way of mapping EFI regions into swapper_pg_dir
using ioremap() and init_memory_mapping(). This feature can be enabled by
passing "efi=old_map" as kernel command line argument. But,
efi_unmap_pages() unmaps EFI boot services code/data regions *only* from
efi_pgd and hence cannot be used for unmapping EFI boot services code/data
regions from swapper_pg_dir.

Introduce a temporary fix to not unmap EFI boot services code/data regions
when EFI_OLD_MEMMAP is enabled while working on a real fix.

EFI_MIXED_MODE is another feature where a 64-bit kernel runs on a
64-bit platform crippled by a 32-bit firmware. To support EFI_MIXED_MODE,
all RAM (i.e. namely EFI regions like EFI_CONVENTIONAL_MEMORY,
EFI_LOADER_<CODE/DATA>, EFI_BOOT_SERVICES_<CODE/DATA> and
EFI_RUNTIME_CODE/DATA regions) is mapped into efi_pgd all the time to
facilitate EFI runtime calls access it's arguments in 1:1 mode. Hence,
don't unmap EFI boot services code/data regions when booted in mixed mode.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Bhupesh Sharma <bhsharma@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 arch/x86/platform/efi/quirks.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 09e811b9da26..9c34230aaeae 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -380,6 +380,22 @@ static void __init efi_unmap_pages(efi_memory_desc_t *md)
 	u64 pa = md->phys_addr;
 	u64 va = md->virt_addr;

+	/*
+	 * To Do: Remove this check after adding functionality to unmap EFI boot
+	 * services code/data regions from direct mapping area because
+	 * "efi=old_map" maps EFI regions in swapper_pg_dir.
+	 */
+	if (efi_enabled(EFI_OLD_MEMMAP))
+		return;
+
+	/*
+	 * EFI mixed mode has all RAM mapped to access arguments while making
+	 * EFI runtime calls, hence don't unmap EFI boot services code/data
+	 * regions.
+	 */
+	if (!efi_is_native() && IS_ENABLED(CONFIG_EFI_MIXED))
+		return;
+
 	if (kernel_unmap_pages_in_pgd(pgd, pa, md->num_pages))
 		pr_err("Failed to unmap 1:1 mapping for 0x%llx\n", pa);

-- 
2.19.1