linux-kernel - [tip: x86/sev] x86/sev: Don't emit BSS_DECRYPTED section unless it is in use

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Message-ID: <176986857025.2495410.14721949712327661606.tip-bot2@tip-bot2>
Date: Sat, 31 Jan 2026 14:09:30 -0000
From: "tip-bot2 for Ard Biesheuvel" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, "Borislav Petkov (AMD)" <bp@...en8.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/sev] x86/sev: Don't emit BSS_DECRYPTED section unless it is in use

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     8c89d3ad3095808ac130c535ad7ed3d1344d5986
Gitweb:        https://git.kernel.org/tip/8c89d3ad3095808ac130c535ad7ed3d1344d5986
Author:        Ard Biesheuvel <ardb@...nel.org>
AuthorDate:    Thu, 08 Jan 2026 09:25:29 
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Sat, 31 Jan 2026 14:42:53 +01:00

x86/sev: Don't emit BSS_DECRYPTED section unless it is in use

The BSS_DECRYPTED section that gets emitted into .bss will be empty if
CONFIG_AMD_MEM_ENCRYPT is not defined. However, due to the fact that it
is injected into .bss rather than emitted as a separate section, the
2 MiB alignment that it specifies is still taken into account
unconditionally, pushing .bss out to the next 2 MiB boundary, leaving
a gap that is never freed.

So only emit a non-empty BSS_DECRYPTED section if it is going to be
used.  In that case, it would still be nice to free the padding, but
that is left for later.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://patch.msgid.link/20260108092526.28586-23-ardb@kernel.org
---
 arch/x86/kernel/vmlinux.lds.S | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index d7af4a6..3a24a3f 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -67,7 +67,18 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
 
 #define ALIGN_ENTRY_TEXT_BEGIN	. = ALIGN(PMD_SIZE);
 #define ALIGN_ENTRY_TEXT_END	. = ALIGN(PMD_SIZE);
+#else
+
+#define X86_ALIGN_RODATA_BEGIN
+#define X86_ALIGN_RODATA_END					\
+		. = ALIGN(PAGE_SIZE);				\
+		__end_rodata_aligned = .;
 
+#define ALIGN_ENTRY_TEXT_BEGIN
+#define ALIGN_ENTRY_TEXT_END
+#endif
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
 /*
  * This section contains data which will be mapped as decrypted. Memory
  * encryption operates on a page basis. Make this section PMD-aligned
@@ -88,17 +99,9 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
 	__pi___end_bss_decrypted = .;				\
 
 #else
-
-#define X86_ALIGN_RODATA_BEGIN
-#define X86_ALIGN_RODATA_END					\
-		. = ALIGN(PAGE_SIZE);				\
-		__end_rodata_aligned = .;
-
-#define ALIGN_ENTRY_TEXT_BEGIN
-#define ALIGN_ENTRY_TEXT_END
 #define BSS_DECRYPTED
-
 #endif
+
 #if defined(CONFIG_X86_64) && defined(CONFIG_KEXEC_CORE)
 #define KEXEC_RELOCATE_KERNEL					\
 	. = ALIGN(0x100);					\