Clang builds with defconfig started crashing after commit fb43d6cb91ef
("x86/mm: Do not auto-massage page protections")
This was caused by introducing a new global access in __startup_64().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 adjusted using fixup_pointer(). Signed-off-by: Alexander Potapenko <[email protected]> Fixes: fb43d6cb91ef ("x86/mm: Do not auto-massage page protections") --- v2: better patch description, added a comment to __startup_64() --- arch/x86/kernel/head64.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 0c408f8c4ed4..9223792f6d0e 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -104,6 +104,13 @@ static bool __head check_la57_support(unsigned long physaddr) } #endif + +/* 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 adjusted using fixup_pointer(). + */ unsigned long __head __startup_64(unsigned long physaddr, struct boot_params *bp) { @@ -113,6 +120,7 @@ unsigned long __head __startup_64(unsigned long physaddr, p4dval_t *p4d; pudval_t *pud; pmdval_t *pmd, pmd_entry; + pteval_t *mask_ptr; bool la57; int i; unsigned int *next_pgt_ptr; @@ -196,7 +204,8 @@ unsigned long __head __startup_64(unsigned long physaddr, pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL; /* Filter out unsupported __PAGE_KERNEL_* bits: */ - pmd_entry &= __supported_pte_mask; + mask_ptr = (pteval_t *)fixup_pointer(&__supported_pte_mask, physaddr); + pmd_entry &= *mask_ptr; pmd_entry += sme_get_me_mask(); pmd_entry += physaddr; -- 2.17.0.441.gb46fe60e1d-goog
