linux-kernel - [PATCH] x86/mm+efi: Avoid creating W+X mappings

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Date:   Thu, 22 Sep 2022 12:31:57 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-efi@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86/mm+efi: Avoid creating W+X mappings

From: Peter Zijlstra <peterz@...radead.org>

I'm planning on sticking this in x86/mm so that it goes upstream
along with the W+X detection code.

--

A recent x86/mm change warns and refuses to create W+X mappings.

The 32-bit EFI code tries to create such a mapping and trips over
the new W+X refusal.

Make the EFI_RUNTIME_SERVICES_CODE mapping read-only to fix it.

Reported-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Tested-by: Guenter Roeck <linux@...ck-us.net>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Darren Hart <dvhart@...radead.org>
Cc: Andy Shevchenko <andy@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org
Cc: linux-efi@...r.kernel.org
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: https://lore.kernel.org/all/d8cd7c7e-24c1-7f70-24a9-91c77aa634af@roeck-us.net/
---
 arch/x86/platform/efi/efi_32.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
index e06a199423c0..d81e379fcd43 100644
--- a/arch/x86/platform/efi/efi_32.c
+++ b/arch/x86/platform/efi/efi_32.c
@@ -136,6 +136,7 @@ void __init efi_runtime_update_mappings(void)
 			if (md->type != EFI_RUNTIME_SERVICES_CODE)
 				continue;
 
+			set_memory_ro(md->virt_addr, md->num_pages);
 			set_memory_x(md->virt_addr, md->num_pages);
 		}
 	}
-- 
2.34.1