From: Alexander Potapenko Date: Wed, 9 May 2018 09:18:22 +0000 (+0200) Subject: x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte_mask' X-Git-Tag: Ubuntu-5.2.0-15.16~4397^2~20 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=4a09f0210c8b1221aae8afda8bd3a603fece0986;p=mirror_ubuntu-eoan-kernel.git x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte_mask' Clang builds with defconfig started crashing after the following 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 Reviewed-by: Dave Hansen Acked-by: Thomas Gleixner Cc: Linus Torvalds Cc: Peter Zijlstra Cc: dvyukov@google.com Cc: kirill.shutemov@linux.intel.com Cc: linux-mm@kvack.org Cc: md@google.com Cc: mka@chromium.org Fixes: fb43d6cb91ef ("x86/mm: Do not auto-massage page protections") Link: http://lkml.kernel.org/r/20180509091822.191810-1-glider@google.com Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 0c408f8c4ed4..2d29e47c056e 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -104,6 +104,12 @@ 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 +119,7 @@ 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 +203,8 @@ 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 = fixup_pointer(&__supported_pte_mask, physaddr); + pmd_entry &= *mask_ptr; pmd_entry += sme_get_me_mask(); pmd_entry += physaddr;