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

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Clang builds with defconfig started crashing after the following
commit:

  fb43d6cb91 ("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: fb43d6cb91 ("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>
This commit is contained in:
Alexander Potapenko 2018-05-09 11:18:22 +02:00 committed by Ingo Molnar
parent 4fe875e4bd
commit 4a09f0210c
1 changed files with 9 additions and 1 deletions
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10
arch/x86/kernel/head64.c
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@ -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;