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Dec 2025 13:20:18 +0000 Message-ID: Date: Sat, 20 Dec 2025 08:19:48 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v2 5/7] mm: introduce BPF kfunc to access memory events To: Roman Gushchin , bot+bpf-ci@kernel.org Cc: bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, inwardvessel@gmail.com, ast@kernel.org, daniel@iogearbox.net, shakeel.butt@linux.dev, mhocko@kernel.org, hannes@cmpxchg.org, andrii@kernel.org, martin.lau@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, ihor.solodrai@linux.dev References: <20251220041250.372179-6-roman.gushchin@linux.dev> <8f23848b8ac657b4b4a2da04da242039c59e9ad9826a8d5fa0f5aee55acfecc9@mail.kernel.org> <87a4zdepdh.fsf@linux.dev> From: Chris Mason Content-Language: en-US In-Reply-To: <87a4zdepdh.fsf@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BL1PR13CA0027.namprd13.prod.outlook.com (2603:10b6:208:256::32) To LV3PR15MB6455.namprd15.prod.outlook.com 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engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-20_03,2025-12-19_02,2025-10-01_01 On 12/19/25 11:41 PM, Roman Gushchin wrote: > bot+bpf-ci@kernel.org writes: > >>> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c >>> index d84fe6f3ed43..858eb43766ce 100644 >>> --- a/mm/bpf_memcontrol.c >>> +++ b/mm/bpf_memcontrol.c >>> @@ -103,6 +103,22 @@ __bpf_kfunc unsigned long bpf_mem_cgroup_usage(struct mem_cgroup *memcg) >>> return mem_cgroup_usage(memcg, false) * PAGE_SIZE; >>> } >>> >>> +/** >>> + * bpf_mem_cgroup_memory_events - Read memory cgroup's memory event value >>> + * @memcg: memory cgroup >>> + * @event: memory event id >>> + * >>> + * Returns current memory event count. >>> + */ >>> +__bpf_kfunc unsigned long bpf_mem_cgroup_memory_events(struct mem_cgroup *memcg, >>> + enum memcg_memory_event event) >>> +{ >>> + if (event >= MEMCG_NR_MEMORY_EVENTS) >>> + return (unsigned long)-1; >> >> Should this also check for negative values? The enum type is typically >> signed, so a BPF program passing a negative event value would pass this >> check but cause an out-of-bounds read from memcg->memory_events[]. >> >> The similar bpf_mem_cgroup_page_state() in this same file uses: >> >> if (idx < 0 || idx >= MEMCG_NR_STAT) >> >> which checks both bounds. Could the check here be changed to: >> >> if (event < 0 || event >= MEMCG_NR_MEMORY_EVENTS) >> >> to match that pattern? > > No, the bpf verifier enforces event > 0. > It's a false positive. I'll add some words here to the bpf prompts, thanks Roman. -chris