Messages in this thread |  | | From | Alexander Potapenko <> | Date | Wed, 16 Aug 2017 21:15:27 +0200 | Subject | Re: [PATCH] x86/boot/64: clang: use fixup_pointer() to access next_early_pgt |
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On Wed, Aug 16, 2017 at 9:08 PM, Alexander Potapenko <glider@google.com> wrote: > __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. > > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Cc: Dmitry Vyukov <dvyukov@google.com> > Cc: Michael Davidson <md@google.com> > Fixes: c88d71508e36 ("x86/boot/64: Rewrite startup_64() in C") > Signed-off-by: Alexander Potapenko <glider@google.com> > --- > arch/x86/kernel/head64.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c > index 46c3c73e7f43..9ba79543d9ee 100644 > --- a/arch/x86/kernel/head64.c > +++ b/arch/x86/kernel/head64.c > @@ -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); > -- > 2.14.1.480.gb18f417b89-goog >
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