Re: [PATCH v3] powerpc/64s/pgtable: fix an undefined behaviour

[Qian Cai]

> On Mar 6, 2020, at 1:56 AM, Christophe Leroy <christophe.leroy@xxxxxx> wrote:
> 
> 
> 
> Le 06/03/2020 Ã 05:48, Qian Cai a Ãcrit :
>> Booting a power9 server with hash MMU could trigger an undefined
>> behaviour because pud_offset(p4d, 0) will do,
>> 0 >> (PAGE_SHIFT:16 + PTE_INDEX_SIZE:8 + H_PMD_INDEX_SIZE:10)
>> Fix it by converting pud_index() and friends to static inline
>> functions.
>> UBSAN: shift-out-of-bounds in arch/powerpc/mm/ptdump/ptdump.c:282:15
>> shift exponent 34 is too large for 32-bit type 'int'
>> CPU: 6 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-20200303+ #13
>> Call Trace:
>> dump_stack+0xf4/0x164 (unreliable)
>> ubsan_epilogue+0x18/0x78
>> __ubsan_handle_shift_out_of_bounds+0x160/0x21c
>> walk_pagetables+0x2cc/0x700
>> walk_pud at arch/powerpc/mm/ptdump/ptdump.c:282
>> (inlined by) walk_pagetables at arch/powerpc/mm/ptdump/ptdump.c:311
>> ptdump_check_wx+0x8c/0xf0
>> mark_rodata_ro+0x48/0x80
>> kernel_init+0x74/0x194
>> ret_from_kernel_thread+0x5c/0x74
>> Suggested-by: Christophe Leroy <christophe.leroy@xxxxxx>
>> Signed-off-by: Qian Cai <cai@xxxxxx>
> 
> Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxx>

Michael, can you take a look at this patch when you have a chance? It looks falling through the cracks.

> 
>> ---
>> v3: convert pud_index() etc to static inline functions.
>> v2: convert pud_offset() etc to static inline functions.
>>  arch/powerpc/include/asm/book3s/64/pgtable.h | 23 ++++++++++++++++----
>>  1 file changed, 19 insertions(+), 4 deletions(-)
>> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> index 201a69e6a355..bd432c6706b9 100644
>> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
>> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> @@ -998,10 +998,25 @@ extern struct page *pgd_page(pgd_t pgd);
>>  #define pud_page_vaddr(pud)	__va(pud_val(pud) & ~PUD_MASKED_BITS)
>>  #define pgd_page_vaddr(pgd)	__va(pgd_val(pgd) & ~PGD_MASKED_BITS)
>>  -#define pgd_index(address) (((address) >> (PGDIR_SHIFT)) & (PTRS_PER_PGD - 1))
>> -#define pud_index(address) (((address) >> (PUD_SHIFT)) & (PTRS_PER_PUD - 1))
>> -#define pmd_index(address) (((address) >> (PMD_SHIFT)) & (PTRS_PER_PMD - 1))
>> -#define pte_index(address) (((address) >> (PAGE_SHIFT)) & (PTRS_PER_PTE - 1))
>> +static inline unsigned long pgd_index(unsigned long address)
>> +{
>> +	return (address >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
>> +}
>> +
>> +static inline unsigned long pud_index(unsigned long address)
>> +{
>> +	return (address >> PUD_SHIFT) & (PTRS_PER_PUD - 1);
>> +}
>> +
>> +static inline unsigned long pmd_index(unsigned long address)
>> +{
>> +	return (address >> PMD_SHIFT) & (PTRS_PER_PMD - 1);
>> +}
>> +
>> +static inline unsigned long pte_index(unsigned long address)
>> +{
>> +	return (address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
>> +}
>>    /*
>>   * Find an entry in a page-table-directory.  We combine the address region