linux-kernel - [PATCH v5 1/7] x86/mm: Decouple MAX_PHYSMEM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250520104138.2734372-10-ardb+git@google.com>
Date: Tue, 20 May 2025 12:41:40 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Brian Gerst <brgerst@...il.com>, 
	"Kirill A. Shutemov" <kirill@...temov.name>, Borislav Petkov <bp@...en8.de>
Subject: [PATCH v5 1/7] x86/mm: Decouple MAX_PHYSMEM_BITS from LA57 state

From: Ard Biesheuvel <ardb@...nel.org>

As the Intel SDM states, MAXPHYADDR is up to 52 bits when running in
long mode, and this is independent from the number of levels of paging.
I.e., it is permitted for a 4-level hierarchy to use 52-bit output
addresses in the descriptors, both for next-level tables and for the
mappings themselves.

So set MAX_PHYSMEM_BITS to 52 in all cases for x86_64, and drop the
MAX_POSSIBLE_PHYSMEM_BITS definition, which becomes redundant as a
result.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/include/asm/pgtable_64_types.h | 2 --
 arch/x86/include/asm/sparsemem.h        | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 4604f924d8b8..1481b234465a 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -56,8 +56,6 @@ extern unsigned int ptrs_per_p4d;
 #define P4D_SIZE		(_AC(1, UL) << P4D_SHIFT)
 #define P4D_MASK		(~(P4D_SIZE - 1))
 
-#define MAX_POSSIBLE_PHYSMEM_BITS	52
-
 /*
  * 3rd level page
  */
diff --git a/arch/x86/include/asm/sparsemem.h b/arch/x86/include/asm/sparsemem.h
index 3918c7a434f5..550b6d73ae22 100644
--- a/arch/x86/include/asm/sparsemem.h
+++ b/arch/x86/include/asm/sparsemem.h
@@ -26,7 +26,7 @@
 # endif
 #else /* CONFIG_X86_32 */
 # define SECTION_SIZE_BITS	27 /* matt - 128 is convenient right now */
-# define MAX_PHYSMEM_BITS	(pgtable_l5_enabled() ? 52 : 46)
+# define MAX_PHYSMEM_BITS	52
 #endif
 
 #endif /* CONFIG_SPARSEMEM */
-- 
2.49.0.1101.gccaa498523-goog