linux-kernel - Re: [PATCH -next v2] powerpc/64s/pgtable: fix an undefined behaviour

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Message-Id: <A40C59F0-B4E2-4A6B-B3AF-0173C93DEB9C@lca.pw>
Date:   Thu, 5 Mar 2020 23:50:51 -0500
From:   Qian Cai <cai@....pw>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>, rashmicy@...il.com,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] powerpc/64s/pgtable: fix an undefined behaviour



> On Mar 5, 2020, at 2:22 PM, Christophe Leroy <christophe.leroy@....fr> wrote:
> 
> 
> 
> Le 05/03/2020 à 15:32, Qian Cai a écrit :
>> 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_offset() and friends to static inline
>> functions.
> 
> I was suggesting to convert pud_index() to static inline, because that's where the shift sits. Is it not possible ?
> 
> Here you seems to fix the problem for now, but if someone reuses pud_index() in another macro one day, the same problem may happen again.
> 

Sounds reasonable. I send out a v3,

https://lore.kernel.org/lkml/20200306044852.3236-1-cai@lca.pw/T/#u

> Christophe
> 
>>  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@....fr>
>> Signed-off-by: Qian Cai <cai@....pw>
>> ---
>>  arch/powerpc/include/asm/book3s/64/pgtable.h | 20 ++++++++++++++------
>>  1 file changed, 14 insertions(+), 6 deletions(-)
>> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> index fa60e8594b9f..4967bc9e25e2 100644
>> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
>> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> @@ -1016,12 +1016,20 @@ static inline bool p4d_access_permitted(p4d_t p4d, bool write)
>>    #define pgd_offset(mm, address)	 ((mm)->pgd + pgd_index(address))
>>  -#define pud_offset(p4dp, addr)	\
>> -	(((pud_t *) p4d_page_vaddr(*(p4dp))) + pud_index(addr))
>> -#define pmd_offset(pudp,addr) \
>> -	(((pmd_t *) pud_page_vaddr(*(pudp))) + pmd_index(addr))
>> -#define pte_offset_kernel(dir,addr) \
>> -	(((pte_t *) pmd_page_vaddr(*(dir))) + pte_index(addr))
>> +static inline pud_t *pud_offset(p4d_t *p4d, unsigned long address)
>> +{
>> +	return (pud_t *)p4d_page_vaddr(*p4d) + pud_index(address);
>> +}
>> +
>> +static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
>> +{
>> +	return (pmd_t *)pud_page_vaddr(*pud) + pmd_index(address);
>> +}
>> +
>> +static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long address)
>> +{
>> +	return (pte_t *)pmd_page_vaddr(*pmd) + pte_index(address);
>> +}
>>    #define pte_offset_map(dir,addr)	pte_offset_kernel((dir), (addr))
>>