[RFC PATCH PoC 04/11] x86/boot: Add a bunch of PI aliases

Ard Biesheuvel
2025-04-23T11:10:44Z

Add aliases for all the data objects that the startup code references -
this is needed so that this code can be moved into its own confined area
where it can only access symbols that have a __pi_ prefix.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/coco/core.c | 2 ++
arch/x86/kernel/cpu/common.c | 1 +
arch/x86/kernel/head64.c | 7 +++++++
arch/x86/kernel/head_64.S | 8 ++++++++
arch/x86/kernel/setup.c | 1 +
arch/x86/kernel/vmlinux.lds.S | 4 ++++
arch/x86/lib/retpoline.S | 1 +
arch/x86/mm/mem_encrypt_amd.c | 2 ++
arch/x86/mm/pgtable.c | 1 +
9 files changed, 27 insertions(+)

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index 9a0ddda3aa69..303360508a71 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -18,7 +18,9 @@
#include <asm/processor.h>

enum cc_vendor cc_vendor __ro_after_init = CC_VENDOR_NONE;
+SYM_PI_ALIAS(cc_vendor);
u64 cc_mask __ro_after_init;
+SYM_PI_ALIAS(cc_mask);

static struct cc_attr_flags {
__u64 host_sev_snp : 1,
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 12126adbc3a9..8fe2e9859c4b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -242,6 +242,7 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
#endif
} };
EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);
+SYM_PI_ALIAS(gdt_page);

#ifdef CONFIG_X86_64
static int __init x86_nopcid_setup(char *s)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 29226f3ac064..b251186a819e 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -48,23 +48,30 @@
*/
extern pmd_t early_dynamic_pgts[EARLY_DYNAMIC_PAGE_TABLES][PTRS_PER_PMD];
unsigned int __initdata next_early_pgt;
+SYM_PI_ALIAS(next_early_pgt);
pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);

#ifdef CONFIG_X86_5LEVEL
unsigned int __pgtable_l5_enabled __ro_after_init;
+SYM_PI_ALIAS(__pgtable_l5_enabled);
unsigned int pgdir_shift __ro_after_init = 39;
EXPORT_SYMBOL(pgdir_shift);
+SYM_PI_ALIAS(pgdir_shift);
unsigned int ptrs_per_p4d __ro_after_init = 1;
EXPORT_SYMBOL(ptrs_per_p4d);
+SYM_PI_ALIAS(ptrs_per_p4d);
#endif

#ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT
unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;
EXPORT_SYMBOL(page_offset_base);
+SYM_PI_ALIAS(page_offset_base);
unsigned long vmalloc_base __ro_after_init = __VMALLOC_BASE_L4;
EXPORT_SYMBOL(vmalloc_base);
+SYM_PI_ALIAS(vmalloc_base);
unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
EXPORT_SYMBOL(vmemmap_base);
+SYM_PI_ALIAS(vmemmap_base);
#endif

/* Wipe all early page tables except for the kernel symbol map */
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index fefe2a25cf02..0c0d38ebf70b 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -573,6 +573,7 @@ SYM_CODE_START_NOALIGN(vc_no_ghcb)
/* Pure iret required here - don't use INTERRUPT_RETURN */
iretq
SYM_CODE_END(vc_no_ghcb)
+SYM_PI_ALIAS(vc_no_ghcb);
#endif

#ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION
@@ -604,10 +605,12 @@ SYM_DATA_START_PTI_ALIGNED(early_top_pgt)
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
.fill PTI_USER_PGD_FILL,8,0
SYM_DATA_END(early_top_pgt)
+SYM_PI_ALIAS(early_top_pgt)

SYM_DATA_START_PAGE_ALIGNED(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
SYM_DATA_END(early_dynamic_pgts)
+SYM_PI_ALIAS(early_dynamic_pgts);

SYM_DATA(early_recursion_flag, .long 0)

@@ -651,6 +654,7 @@ SYM_DATA_START_PAGE_ALIGNED(level4_kernel_pgt)
.fill 511,8,0
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
SYM_DATA_END(level4_kernel_pgt)
+SYM_PI_ALIAS(level4_kernel_pgt)
#endif

SYM_DATA_START_PAGE_ALIGNED(level3_kernel_pgt)
@@ -659,6 +663,7 @@ SYM_DATA_START_PAGE_ALIGNED(level3_kernel_pgt)
.quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
SYM_DATA_END(level3_kernel_pgt)
+SYM_PI_ALIAS(level3_kernel_pgt)

SYM_DATA_START_PAGE_ALIGNED(level2_kernel_pgt)
/*
@@ -676,6 +681,7 @@ SYM_DATA_START_PAGE_ALIGNED(level2_kernel_pgt)
*/
PMDS(0, __PAGE_KERNEL_LARGE_EXEC, KERNEL_IMAGE_SIZE/PMD_SIZE)
SYM_DATA_END(level2_kernel_pgt)
+SYM_PI_ALIAS(level2_kernel_pgt)

SYM_DATA_START_PAGE_ALIGNED(level2_fixmap_pgt)
.fill (512 - 4 - FIXMAP_PMD_NUM),8,0
@@ -688,6 +694,7 @@ SYM_DATA_START_PAGE_ALIGNED(level2_fixmap_pgt)
/* 6 MB reserved space + a 2MB hole */
.fill 4,8,0
SYM_DATA_END(level2_fixmap_pgt)
+SYM_PI_ALIAS(level2_fixmap_pgt)

SYM_DATA_START_PAGE_ALIGNED(level1_fixmap_pgt)
.rept (FIXMAP_PMD_NUM)
@@ -703,6 +710,7 @@ SYM_DATA(smpboot_control, .long 0)
.align 16
/* This must match the first entry in level2_kernel_pgt */
SYM_DATA(phys_base, .quad 0x0)
+SYM_PI_ALIAS(phys_base);
EXPORT_SYMBOL(phys_base)

#include "../xen/xen-head.S"
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 9d2a13b37833..ae1fdb0fc6ba 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -134,6 +134,7 @@ struct ist_info ist_info;

struct cpuinfo_x86 boot_cpu_data __read_mostly;
EXPORT_SYMBOL(boot_cpu_data);
+SYM_PI_ALIAS(boot_cpu_data);

#if !defined(CONFIG_X86_PAE) || defined(CONFIG_X86_64)
__visible unsigned long mmu_cr4_features __ro_after_init;
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ccdc45e5b759..9340c74b680d 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -79,11 +79,13 @@ const_cpu_current_top_of_stack = cpu_current_top_of_stack;
#define BSS_DECRYPTED \
. = ALIGN(PMD_SIZE); \
__start_bss_decrypted = .; \
+ __pi___start_bss_decrypted = .; \
*(.bss..decrypted); \
. = ALIGN(PAGE_SIZE); \
__start_bss_decrypted_unused = .; \
. = ALIGN(PMD_SIZE); \
__end_bss_decrypted = .; \
+ __pi___end_bss_decrypted = .; \

#else

@@ -128,6 +130,7 @@ SECTIONS
/* Text and read-only data */
.text : AT(ADDR(.text) - LOAD_OFFSET) {
_text = .;
+ __pi__text = .;
_stext = .;
ALIGN_ENTRY_TEXT_BEGIN
*(.text..__x86.rethunk_untrain)
@@ -391,6 +394,7 @@ SECTIONS

. = ALIGN(PAGE_SIZE); /* keep VO_INIT_SIZE page aligned */
_end = .;
+ __pi__end = .;

#ifdef CONFIG_AMD_MEM_ENCRYPT
/*
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index a26c43abd47d..cabec2788e70 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -394,6 +394,7 @@ SYM_CODE_START(__x86_return_thunk)
#endif
int3
SYM_CODE_END(__x86_return_thunk)
+SYM_PI_ALIAS(__x86_return_thunk)
EXPORT_SYMBOL(__x86_return_thunk)

#endif /* CONFIG_MITIGATION_RETHUNK */
diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index 7490ff6d83b1..9aaeda6eb83d 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/arch/x86/mm/mem_encrypt_amd.c
@@ -40,7 +40,9 @@
* section is later cleared.
*/
u64 sme_me_mask __section(".data") = 0;
+SYM_PI_ALIAS(sme_me_mask);
u64 sev_status __section(".data") = 0;
+SYM_PI_ALIAS(sev_status);
u64 sev_check_data __section(".data") = 0;
EXPORT_SYMBOL(sme_me_mask);

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index a05fcddfc811..9e26215da18d 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -10,6 +10,7 @@
#ifdef CONFIG_DYNAMIC_PHYSICAL_MASK
phys_addr_t physical_mask __ro_after_init = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
EXPORT_SYMBOL(physical_mask);
+SYM_PI_ALIAS(physical_mask);
#endif

pgtable_t pte_alloc_one(struct mm_struct *mm)
--
2.49.0.805.g082f7c87e0-goog