Commit dafb26f4 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

x86/boot: Drop RIP_REL_REF() uses from early mapping code 



Now that __startup_64() is built using -fPIC, RIP_REL_REF() has become a
NOP and can be removed. Only some occurrences of rip_rel_ptr() will
remain, to explicitly take the address of certain global structures in
the 1:1 mapping of memory.

While at it, update the code comment to describe why this is needed.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo 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/20250410134117.3713574-17-ardb+git@google.com
parent dbe0ad77

arch/x86/boot/startup/map_kernel.c

+21 −20
Original line number Diff line number Diff line
@@ -26,12 +26,12 @@ static inline bool check_la57_support(void) 
	if (!(native_read_cr4() & X86_CR4_LA57))

		return false;



	RIP_REL_REF(__pgtable_l5_enabled)	= 1;

	RIP_REL_REF(pgdir_shift)		= 48;

	RIP_REL_REF(ptrs_per_p4d)		= 512;

	RIP_REL_REF(page_offset_base)		= __PAGE_OFFSET_BASE_L5;

	RIP_REL_REF(vmalloc_base)		= __VMALLOC_BASE_L5;

	RIP_REL_REF(vmemmap_base)		= __VMEMMAP_BASE_L5;

	__pgtable_l5_enabled	= 1;

	pgdir_shift		= 48;

	ptrs_per_p4d		= 512;

	page_offset_base	= __PAGE_OFFSET_BASE_L5;

	vmalloc_base		= __VMALLOC_BASE_L5;

	vmemmap_base		= __VMEMMAP_BASE_L5;



	return true;

}
@@ -81,12 +81,14 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp, 
	return sme_get_me_mask();

}



/* Code in __startup_64() can be relocated during execution, but the compiler

 * doesn't have to generate PC-relative relocations when accessing globals from

 * that function. Clang actually does not generate them, which leads to

 * boot-time crashes. To work around this problem, every global pointer must

 * be accessed using RIP_REL_REF(). Kernel virtual addresses can be determined

 * by subtracting p2v_offset from the RIP-relative address.

/*

 * This code is compiled using PIC codegen because it will execute from the

 * early 1:1 mapping of memory, which deviates from the mapping expected by the

 * linker. Due to this deviation, taking the address of a global variable will

 * produce an ambiguous result when using the plain & operator.  Instead,

 * rip_rel_ptr() must be used, which will return the RIP-relative address in

 * the 1:1 mapping of memory. Kernel virtual addresses can be determined by

 * subtracting p2v_offset from the RIP-relative address.

 */

unsigned long __head __startup_64(unsigned long p2v_offset,

				  struct boot_params *bp)
@@ -113,8 +115,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset, 
	 * Compute the delta between the address I am compiled to run at

	 * and the address I am actually running at.

	 */

	load_delta = __START_KERNEL_map + p2v_offset;

	RIP_REL_REF(phys_base) = load_delta;

	phys_base = load_delta = __START_KERNEL_map + p2v_offset;



	/* Is the address not 2M aligned? */

	if (load_delta & ~PMD_MASK)
@@ -138,11 +139,11 @@ unsigned long __head __startup_64(unsigned long p2v_offset, 
		pgd[pgd_index(__START_KERNEL_map)] = (pgdval_t)p4d | _PAGE_TABLE;

	}



	RIP_REL_REF(level3_kernel_pgt)[PTRS_PER_PUD - 2].pud += load_delta;

	RIP_REL_REF(level3_kernel_pgt)[PTRS_PER_PUD - 1].pud += load_delta;

	level3_kernel_pgt[PTRS_PER_PUD - 2].pud += load_delta;

	level3_kernel_pgt[PTRS_PER_PUD - 1].pud += load_delta;



	for (i = FIXMAP_PMD_TOP; i > FIXMAP_PMD_TOP - FIXMAP_PMD_NUM; i--)

		RIP_REL_REF(level2_fixmap_pgt)[i].pmd += load_delta;

		level2_fixmap_pgt[i].pmd += load_delta;



	/*

	 * Set up the identity mapping for the switchover.  These
@@ -153,12 +154,12 @@ unsigned long __head __startup_64(unsigned long p2v_offset, 


	pud = &early_pgts[0]->pmd;

	pmd = &early_pgts[1]->pmd;

	RIP_REL_REF(next_early_pgt) = 2;

	next_early_pgt = 2;



	pgtable_flags = _KERNPG_TABLE_NOENC + sme_get_me_mask();



	if (la57) {

		p4d = &early_pgts[RIP_REL_REF(next_early_pgt)++]->pmd;

		p4d = &early_pgts[next_early_pgt++]->pmd;



		i = (physaddr >> PGDIR_SHIFT) % PTRS_PER_PGD;

		pgd[i + 0] = (pgdval_t)p4d + pgtable_flags;
@@ -179,7 +180,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset, 


	pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL;

	/* Filter out unsupported __PAGE_KERNEL_* bits: */

	pmd_entry &= RIP_REL_REF(__supported_pte_mask);

	pmd_entry &= __supported_pte_mask;

	pmd_entry += sme_get_me_mask();

	pmd_entry +=  physaddr;