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

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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: 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/20250410134117.3713574-17-ardb+git@google.com
This commit is contained in:
Ard Biesheuvel
2025-04-10 15:41:22 +02:00
committed by Ingo Molnar
parent dbe0ad775c
commit dafb26f427
1 changed files with 21 additions and 20 deletions
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41
arch/x86/boot/startup/map_kernel.c
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@@ -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;