* [PATCH v2 2/2] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED
2026-06-23 15:24 [PATCH v2 1/2] x86/build: only align ENTRY_TEXT to PMD_SIZE if necessary Hamza Mahfooz
@ 2026-06-23 15:24 ` Hamza Mahfooz
2026-07-09 22:36 ` Borislav Petkov
2026-07-09 23:14 ` [tip: x86/cleanups] x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary tip-bot2 for Hamza Mahfooz
2026-07-10 9:30 ` [tip: x86/build] " tip-bot2 for Hamza Mahfooz
2 siblings, 1 reply; 5+ messages in thread
From: Hamza Mahfooz @ 2026-06-23 15:24 UTC (permalink / raw)
To: x86
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen,
H. Peter Anvin, Andy Lutomirski, Peter Zijlstra, Ard Biesheuvel,
Nathan Chancellor, linux-kernel, Hamza Mahfooz, Jared White
This region is unused after mark_rodata_ro() and takes up, up to 2 MiB
of memory. So, free it in mark_rodata_ro().
Co-developed-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
---
arch/x86/include/asm/sections.h | 1 +
arch/x86/kernel/vmlinux.lds.S | 2 ++
arch/x86/mm/init_64.c | 4 ++++
3 files changed, 7 insertions(+)
diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 30e8ee7006f9..1d6589bc0f68 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -8,6 +8,7 @@
extern char __relocate_kernel_start[], __relocate_kernel_end[];
extern char __brk_base[], __brk_limit[];
extern char __end_rodata_aligned[];
+extern char __start_bss_decrypted_gap[];
#if defined(CONFIG_X86_64)
extern char __end_rodata_hpage_align[];
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 53519fa7c772..de9901bda7d0 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -94,6 +94,8 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
* decrypted to avoid exposing more than we wish.
*/
#define BSS_DECRYPTED \
+ . = ALIGN(PAGE_SIZE); \
+ __start_bss_decrypted_gap = .; \
. = ALIGN(PMD_SIZE); \
__start_bss_decrypted = .; \
__pi___start_bss_decrypted = .; \
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index df2261fa4f98..3d90bd593637 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1396,6 +1396,8 @@ void mark_rodata_ro(void)
unsigned long end = (unsigned long)__end_rodata_hpage_align;
unsigned long text_end = PFN_ALIGN(_etext);
unsigned long rodata_end = PFN_ALIGN(__end_rodata);
+ unsigned long bss_decrypted_gap_start = PFN_ALIGN(__start_bss_decrypted_gap);
+ unsigned long bss_decrypted_gap_stop = PFN_ALIGN(__start_bss_decrypted);
unsigned long all_end;
printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
@@ -1433,6 +1435,8 @@ void mark_rodata_ro(void)
(void *)text_end, (void *)rodata_start);
free_kernel_image_pages("unused kernel image (rodata/data gap)",
(void *)rodata_end, (void *)_sdata);
+ free_kernel_image_pages("unused kernel image (bss_decrypted gap)",
+ (void *)bss_decrypted_gap_start, (void *)bss_decrypted_gap_stop);
}
/*
--
2.54.0
^ permalink raw reply [flat|nested] 5+ messages in thread* [tip: x86/cleanups] x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary
2026-06-23 15:24 [PATCH v2 1/2] x86/build: only align ENTRY_TEXT to PMD_SIZE if necessary Hamza Mahfooz
2026-06-23 15:24 ` [PATCH v2 2/2] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED Hamza Mahfooz
@ 2026-07-09 23:14 ` tip-bot2 for Hamza Mahfooz
2026-07-10 9:30 ` [tip: x86/build] " tip-bot2 for Hamza Mahfooz
2 siblings, 0 replies; 5+ messages in thread
From: tip-bot2 for Hamza Mahfooz @ 2026-07-09 23:14 UTC (permalink / raw)
To: linux-tip-commits
Cc: Jared White, Hamza Mahfooz, Borislav Petkov (AMD), x86, linux-kernel
The following commit has been merged into the x86/cleanups branch of tip:
Commit-ID: fa84683b892e2590401e655bebe6ba461367adc7
Gitweb: https://git.kernel.org/tip/fa84683b892e2590401e655bebe6ba461367adc7
Author: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
AuthorDate: Tue, 23 Jun 2026 11:24:29 -04:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Thu, 09 Jul 2026 15:34:23 -07:00
x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary
PTI requires the begin and end of ENTRY_TEXT be aligned to PMD_SIZE. SRSO
requires srso_alias_untrain_ret to be 2M aligned. This costs between 2-4 MiB
of RAM (depending on the size of the preceding section). So, only align when
either of the two are enabled.
Co-developed-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20260623152430.1473481-1-hamzamahfooz@linux.microsoft.com
---
arch/x86/kernel/vmlinux.lds.S | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e336d..10caf92 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -65,9 +65,15 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
__end_rodata_hpage_align = .; \
__end_rodata_aligned = .;
+#if defined(CONFIG_MITIGATION_PAGE_TABLE_ISOLATION) || defined(CONFIG_MITIGATION_SRSO)
#define ALIGN_ENTRY_TEXT_BEGIN . = ALIGN(PMD_SIZE);
#define ALIGN_ENTRY_TEXT_END . = ALIGN(PMD_SIZE);
#else
+#define ALIGN_ENTRY_TEXT_BEGIN
+#define ALIGN_ENTRY_TEXT_END
+#endif
+
+#else
#define X86_ALIGN_RODATA_BEGIN
#define X86_ALIGN_RODATA_END \
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip: x86/build] x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary
2026-06-23 15:24 [PATCH v2 1/2] x86/build: only align ENTRY_TEXT to PMD_SIZE if necessary Hamza Mahfooz
2026-06-23 15:24 ` [PATCH v2 2/2] x86/mm/64: free the gap between BSS_MAIN and BSS_DECRYPTED Hamza Mahfooz
2026-07-09 23:14 ` [tip: x86/cleanups] x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary tip-bot2 for Hamza Mahfooz
@ 2026-07-10 9:30 ` tip-bot2 for Hamza Mahfooz
2 siblings, 0 replies; 5+ messages in thread
From: tip-bot2 for Hamza Mahfooz @ 2026-07-10 9:30 UTC (permalink / raw)
To: linux-tip-commits
Cc: Jared White, Hamza Mahfooz, Borislav Petkov (AMD),
Ingo Molnar, x86, linux-kernel
The following commit has been merged into the x86/build branch of tip:
Commit-ID: f6cff820877ff34839920ff9de9b912359cfb607
Gitweb: https://git.kernel.org/tip/f6cff820877ff34839920ff9de9b912359cfb607
Author: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
AuthorDate: Tue, 23 Jun 2026 11:24:29 -04:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 10 Jul 2026 11:21:17 +02:00
x86/build: Only align ENTRY_TEXT to PMD_SIZE if necessary
PTI requires the begin and end of ENTRY_TEXT be aligned to PMD_SIZE. SRSO
requires srso_alias_untrain_ret to be 2M aligned. This costs between 2-4 MiB
of RAM (depending on the size of the preceding section). So, only align when
either of the two are enabled.
Co-developed-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Jared White <jaredwhite@microsoft.com>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20260623152430.1473481-1-hamzamahfooz@linux.microsoft.com
---
arch/x86/kernel/vmlinux.lds.S | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e336d..10caf92 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -65,9 +65,15 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
__end_rodata_hpage_align = .; \
__end_rodata_aligned = .;
+#if defined(CONFIG_MITIGATION_PAGE_TABLE_ISOLATION) || defined(CONFIG_MITIGATION_SRSO)
#define ALIGN_ENTRY_TEXT_BEGIN . = ALIGN(PMD_SIZE);
#define ALIGN_ENTRY_TEXT_END . = ALIGN(PMD_SIZE);
#else
+#define ALIGN_ENTRY_TEXT_BEGIN
+#define ALIGN_ENTRY_TEXT_END
+#endif
+
+#else
#define X86_ALIGN_RODATA_BEGIN
#define X86_ALIGN_RODATA_END \
^ permalink raw reply [flat|nested] 5+ messages in thread