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Message-ID: <40593b16-8232-27fc-808a-37bad7457dc0@efficios.com>
Date: Mon, 4 Sep 2023 08:58:48 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Denis Arefev <arefev@...mel.ru>,
Lai Jiangshan <jiangshanlai@...il.com>,
"Paul E. McKenney" <paulmck@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>,
Steven Rostedt <rostedt@...dmis.org>, rcu@...r.kernel.org,
lvc-project@...uxtesting.org, linux-kernel@...r.kernel.org,
trufanov@...mel.ru, vfh@...mel.ru,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v3] Fix srcu_struct node grpmask overflow on 64-bit
systems
On 9/4/23 08:42, Mathieu Desnoyers wrote:
> On 9/4/23 08:21, Denis Arefev wrote:
>> The value of an arithmetic expression 1 << (cpu - sdp->mynode->grplo)
>> is subject to overflow due to a failure to cast operands to a larger
>> data type before performing arithmetic.
>>
>> The maximum result of this subtraction is defined by the RCU_FANOUT
>> or other srcu level-spread values assigned by rcu_init_levelspread(),
>> which can indeed cause the signed 32-bit integer literal ("1") to
>> overflow
>> when shifted by any value greater than 31.
>
> We could expand on this:
>
> The maximum result of this subtraction is defined by the RCU_FANOUT
> or other srcu level-spread values assigned by rcu_init_levelspread(),
> which can indeed cause the signed 32-bit integer literal ("1") to overflow
> when shifted by any value greater than 31 on a 64-bit system.
>
> Moreover, when the subtraction value is 31, the 1 << 31 expression results
> in 0xffffffff80000000 when the signed integer is promoted to unsigned long
> on 64-bit systems due to type promotion rules, which is certainly not the
> intended result.
>
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> With the commit message updated with my comment above, please also add:
>
> Fixes: c7e88067c1 ("srcu: Exact tracking of srcu_data structures
> containing callbacks")
> Cc: <stable@...r.kernel.org> # v4.11
Sorry, the line above should read:
Cc: <stable@...r.kernel.org> # v4.11+
Thanks,
Mathieu
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>
> Thanks!
>
> Mathieu
>
>>
>> Signed-off-by: Denis Arefev <arefev@...mel.ru>
>> ---
>> v3: Changed the name of the patch, as suggested by
>> Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> v2: Added fixes to the srcu_schedule_cbs_snp function as suggested by
>> Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> kernel/rcu/srcutree.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
>> index 20d7a238d675..6c18e6005ae1 100644
>> --- a/kernel/rcu/srcutree.c
>> +++ b/kernel/rcu/srcutree.c
>> @@ -223,7 +223,7 @@ static bool init_srcu_struct_nodes(struct
>> srcu_struct *ssp, gfp_t gfp_flags)
>> snp->grplo = cpu;
>> snp->grphi = cpu;
>> }
>> - sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
>> + sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
>> }
>> smp_store_release(&ssp->srcu_sup->srcu_size_state,
>> SRCU_SIZE_WAIT_BARRIER);
>> return true;
>> @@ -833,7 +833,7 @@ static void srcu_schedule_cbs_snp(struct
>> srcu_struct *ssp, struct srcu_node *snp
>> int cpu;
>> for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
>> - if (!(mask & (1 << (cpu - snp->grplo))))
>> + if (!(mask & (1UL << (cpu - snp->grplo))))
>> continue;
>> srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
>> }
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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