Commit 4a09f021 authored May 09, 2018 by Alexander Potapenko Committed by Ingo Molnar May 14, 2018

x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte_mask'



Clang builds with defconfig started crashing after the following
commit:

  fb43d6cb ("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 <glider@google.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: dvyukov@google.com
Cc: kirill.shutemov@linux.intel.com
Cc: linux-mm@kvack.org
Cc: md@google.com
Cc: mka@chromium.org
Fixes: fb43d6cb ("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 <mingo@kernel.org>

parent 4fe875e4

arch/x86/kernel/head64.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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;

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