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Subject: Re: [PATCH -next v2] powerpc/64s/pgtable: fix an undefined behaviour
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <a082f4c3-db68-6ca3-c832-b1abb5363e3a@c-s.fr>
Date:   Thu, 5 Mar 2020 23:50:51 -0500
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Andrew Morton <akpm@linux-foundation.org>, rashmicy@gmail.com,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
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Message-Id: <A40C59F0-B4E2-4A6B-B3AF-0173C93DEB9C@lca.pw>
References: <1583418759-16105-1-git-send-email-cai@lca.pw>
 <a082f4c3-db68-6ca3-c832-b1abb5363e3a@c-s.fr>
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Sender: linux-kernel-owner@vger.kernel.org
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> On Mar 5, 2020, at 2:22 PM, Christophe Leroy <christophe.leroy@c-s.fr> =
wrote:
>=20
>=20
>=20
> Le 05/03/2020 =C3=A0 15:32, Qian Cai a =C3=A9crit :
>> 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.
>=20
> I was suggesting to convert pud_index() to static inline, because =
that's where the shift sits. Is it not possible ?
>=20
> 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.
>=20

Sounds reasonable. I send out a v3,

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

> Christophe
>=20
>>  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@c-s.fr>
>> Signed-off-by: Qian Cai <cai@lca.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))
>> =20