x86/asm: Make rip_rel_ptr() usable from fPIC code

RIP_REL_REF() is used in non-PIC C code that is called very early,
before the kernel virtual mapping is up, which is the mapping that the
linker expects. It is currently used in two different ways:

 - to refer to the value of a global variable, including as an lvalue in
   assignments;

 - to take the address of a global variable via the mapping that the code
   currently executes at.

The former case is only needed in non-PIC code, as PIC code will never
use absolute symbol references when the address of the symbol is not
being used. But taking the address of a variable in PIC code may still
require extra care, as a stack allocated struct assignment may be
emitted as a memcpy() from a statically allocated copy in .rodata.

For instance, this

  void startup_64_setup_gdt_idt(void)
  {
        struct desc_ptr startup_gdt_descr = {
                .address = (__force unsigned long)gdt_page.gdt,
                .size    = GDT_SIZE - 1,
        };

may result in an absolute symbol reference in PIC code, even though the
struct is allocated on the stack and populated at runtime.

To address this case, make rip_rel_ptr() accessible in PIC code, and
update any existing uses where the address of a global variable is
taken using RIP_REL_REF.

Once all code of this nature has been moved into arch/x86/boot/startup
and built with -fPIC, RIP_REL_REF() can be retired, and only
rip_rel_ptr() will remain.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dionna Amalie Glaze <dionnaglaze@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kevin Loughlin <kevinloughlin@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-efi@vger.kernel.org
Link: https://lore.kernel.org/r/20250410134117.3713574-14-ardb+git@google.com

1 files changed, 12 insertions, 12 deletions

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index fa9b6339975f..954d093f187b 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -106,8 +106,8 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
 	 * attribute.
 	 */
 	if (sme_get_me_mask()) {
-		paddr = (unsigned long)&RIP_REL_REF(__start_bss_decrypted);
-		paddr_end = (unsigned long)&RIP_REL_REF(__end_bss_decrypted);
+		paddr = (unsigned long)rip_rel_ptr(__start_bss_decrypted);
+		paddr_end = (unsigned long)rip_rel_ptr(__end_bss_decrypted);
 
 		for (; paddr < paddr_end; paddr += PMD_SIZE) {
 			/*
@@ -144,8 +144,8 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp,
 unsigned long __head __startup_64(unsigned long p2v_offset,
 				  struct boot_params *bp)
 {
-	pmd_t (*early_pgts)[PTRS_PER_PMD] = RIP_REL_REF(early_dynamic_pgts);
-	unsigned long physaddr = (unsigned long)&RIP_REL_REF(_text);
+	pmd_t (*early_pgts)[PTRS_PER_PMD] = rip_rel_ptr(early_dynamic_pgts);
+	unsigned long physaddr = (unsigned long)rip_rel_ptr(_text);
 	unsigned long va_text, va_end;
 	unsigned long pgtable_flags;
 	unsigned long load_delta;
@@ -174,18 +174,18 @@ unsigned long __head __startup_64(unsigned long p2v_offset,
 		for (;;);
 
 	va_text = physaddr - p2v_offset;
-	va_end  = (unsigned long)&RIP_REL_REF(_end) - p2v_offset;
+	va_end  = (unsigned long)rip_rel_ptr(_end) - p2v_offset;
 
 	/* Include the SME encryption mask in the fixup value */
 	load_delta += sme_get_me_mask();
 
 	/* Fixup the physical addresses in the page table */
 
-	pgd = &RIP_REL_REF(early_top_pgt)->pgd;
+	pgd = rip_rel_ptr(early_top_pgt);
 	pgd[pgd_index(__START_KERNEL_map)] += load_delta;
 
 	if (IS_ENABLED(CONFIG_X86_5LEVEL) && la57) {
-		p4d = (p4dval_t *)&RIP_REL_REF(level4_kernel_pgt);
+		p4d = (p4dval_t *)rip_rel_ptr(level4_kernel_pgt);
 		p4d[MAX_PTRS_PER_P4D - 1] += load_delta;
 
 		pgd[pgd_index(__START_KERNEL_map)] = (pgdval_t)p4d | _PAGE_TABLE;
@@ -258,7 +258,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset,
 	 * error, causing the BIOS to halt the system.
 	 */
 
-	pmd = &RIP_REL_REF(level2_kernel_pgt)->pmd;
+	pmd = rip_rel_ptr(level2_kernel_pgt);
 
 	/* invalidate pages before the kernel image */
 	for (i = 0; i < pmd_index(va_text); i++)
@@ -531,7 +531,7 @@ static gate_desc bringup_idt_table[NUM_EXCEPTION_VECTORS] __page_aligned_data;
 static void __head startup_64_load_idt(void *vc_handler)
 {
 	struct desc_ptr desc = {
-		.address = (unsigned long)&RIP_REL_REF(bringup_idt_table),
+		.address = (unsigned long)rip_rel_ptr(bringup_idt_table),
 		.size    = sizeof(bringup_idt_table) - 1,
 	};
 	struct idt_data data;
@@ -565,11 +565,11 @@ void early_setup_idt(void)
  */
 void __head startup_64_setup_gdt_idt(void)
 {
-	struct desc_struct *gdt = (void *)(__force unsigned long)gdt_page.gdt;
+	struct gdt_page *gp = rip_rel_ptr((void *)(__force unsigned long)&gdt_page);
 	void *handler = NULL;
 
 	struct desc_ptr startup_gdt_descr = {
-		.address = (unsigned long)&RIP_REL_REF(*gdt),
+		.address = (unsigned long)gp->gdt,
 		.size    = GDT_SIZE - 1,
 	};
 
@@ -582,7 +582,7 @@ void __head startup_64_setup_gdt_idt(void)
 		     "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
 
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
-		handler = &RIP_REL_REF(vc_no_ghcb);
+		handler = rip_rel_ptr(vc_no_ghcb);
 
 	startup_64_load_idt(handler);
 }