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

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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
This commit is contained in:
Ard Biesheuvel
2025-04-10 15:41:19 +02:00
committed by Ingo Molnar
parent 9e8e879426
commit bcceba3c72
5 changed files with 19 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/coco/sev/core.c
View File

@@ -2400,7 +2400,7 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
* kernel was loaded (physbase), so the get the CA address using
* RIP-relative addressing.
*/
pa = (u64)&RIP_REL_REF(boot_svsm_ca_page);
pa = (u64)rip_rel_ptr(&boot_svsm_ca_page);
/*
* Switch over to the boot SVSM CA while the current CA is still

4
arch/x86/coco/sev/shared.c
View File

@@ -475,7 +475,7 @@ static int sev_cpuid_hv(struct ghcb *ghcb, struct es_em_ctxt *ctxt, struct cpuid
*/
static const struct snp_cpuid_table *snp_cpuid_get_table(void)
{
return &RIP_REL_REF(cpuid_table_copy);
return rip_rel_ptr(&cpuid_table_copy);
}
/*
@@ -1681,7 +1681,7 @@ static bool __head svsm_setup_ca(const struct cc_blob_sev_info *cc_info)
* routine is running identity mapped when called, both by the decompressor
* code and the early kernel code.
*/
if (!rmpadjust((unsigned long)&RIP_REL_REF(boot_ghcb_page), RMP_PG_SIZE_4K, 1))
if (!rmpadjust((unsigned long)rip_rel_ptr(&boot_ghcb_page), RMP_PG_SIZE_4K, 1))
return false;
/*

2
arch/x86/include/asm/asm.h
View File

@@ -114,13 +114,13 @@
#endif
#ifndef __ASSEMBLER__
#ifndef __pic__
static __always_inline __pure void *rip_rel_ptr(void *p)
{
asm("leaq %c1(%%rip), %0" : "=r"(p) : "i"(p));
return p;
}
#ifndef __pic__
#define RIP_REL_REF(var) (*(typeof(&(var)))rip_rel_ptr(&(var)))
#else
#define RIP_REL_REF(var) (var)

24
arch/x86/kernel/head64.c
View File

@@ -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);
}

6
arch/x86/mm/mem_encrypt_identity.c
View File

@@ -318,8 +318,8 @@ void __head sme_encrypt_kernel(struct boot_params *bp)
* memory from being cached.
*/
kernel_start = (unsigned long)RIP_REL_REF(_text);
kernel_end = ALIGN((unsigned long)RIP_REL_REF(_end), PMD_SIZE);
kernel_start = (unsigned long)rip_rel_ptr(_text);
kernel_end = ALIGN((unsigned long)rip_rel_ptr(_end), PMD_SIZE);
kernel_len = kernel_end - kernel_start;
initrd_start = 0;
@@ -345,7 +345,7 @@ void __head sme_encrypt_kernel(struct boot_params *bp)
* pagetable structures for the encryption of the kernel
* pagetable structures for workarea (in case not currently mapped)
*/
execute_start = workarea_start = (unsigned long)RIP_REL_REF(sme_workarea);
execute_start = workarea_start = (unsigned long)rip_rel_ptr(sme_workarea);
execute_end = execute_start + (PAGE_SIZE * 2) + PMD_SIZE;
execute_len = execute_end - execute_start;