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Commit 187e91fe authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Ingo Molnar
Browse files

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



__startup_64() is normally using fixup_pointer() to access globals in a
position-independent fashion. However 'next_early_pgt' was accessed
directly, which wasn't guaranteed to work.

Luckily GCC was generating a R_X86_64_PC32 PC-relative relocation for
'next_early_pgt', but Clang emitted a R_X86_64_32S, which led to
accessing invalid memory and rebooting the kernel.

Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Davidson <md@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c88d7150 ("x86/boot/64: Rewrite startup_64() in C")
Link: http://lkml.kernel.org/r/20170816190808.131748-1-glider@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 01578e36

arch/x86/kernel/head64.c

+4 −3
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ void __head __startup_64(unsigned long physaddr) 
	pudval_t *pud;

	pmdval_t *pmd, pmd_entry;

	int i;

	unsigned int *next_pgt_ptr;



	/* Is the address too large? */

	if (physaddr >> MAX_PHYSMEM_BITS)
@@ -91,9 +92,9 @@ void __head __startup_64(unsigned long physaddr) 
	 * creates a bunch of nonsense entries but that is fine --

	 * it avoids problems around wraparound.

	 */



	pud = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);

	pmd = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);

	next_pgt_ptr = fixup_pointer(&next_early_pgt, physaddr);

	pud = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);

	pmd = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);



	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {

		p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);