[RFC/RFT PATCH 02/19] x86/sev: Don't emit BSS_DECRYPT section unless it is in use

Ard Biesheuvel
2026-01-08T09:28:03Z

The BSS_DECRYPT 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_DECRYPT 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@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 d7af4a64c211..3a24a3fc55f5 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); \
--
2.47.3