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Wed, 06 Jul 2022 08:21:42 -0700 (PDT) X-Google-Smtp-Source: AGRyM1s2+Xffu3s3AfptA3eZWELbrOWi/CqyYzom+y2gsOdu+DMe8X2B0ID45kOQWpCgGgbCy69x8Nld6DIcmyOzSyw= X-Received: by 2002:a67:4347:0:b0:356:37f7:6fa3 with SMTP id q68-20020a674347000000b0035637f76fa3mr24958223vsa.40.1657120901924; Wed, 06 Jul 2022 08:21:41 -0700 (PDT) MIME-Version: 1.0 References: <20220531081412.22db88cc@kernel.org> <1654011382-2453-1-git-send-email-chen45464546@163.com> <20220531084704.480133fa@kernel.org> <3498989.c69f.1811f41186e.Coremail.chen45464546@163.com> In-Reply-To: From: Maurizio Lombardi Date: Wed, 6 Jul 2022 17:21:31 +0200 Message-ID: Subject: Re: Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE To: Alexander Duyck Cc: =?UTF-8?B?5oSa5qCR?= , Jakub Kicinski , Andrew Morton , linux-mm , LKML , Netdev X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable ARC-Seal: i=1; s=arc-20220608; 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dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=hisURBLi; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf02.hostedemail.com: domain of mlombard@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=mlombard@redhat.com X-Stat-Signature: 4krxy63t93983q9ohdjw4iuwd6qtzs11 X-Rspamd-Queue-Id: 868EC8000C X-Rspamd-Server: rspam05 X-Rspam-User: X-HE-Tag: 1657120904-861456 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: st 1. 6. 2022 v 17:05 odes=C3=ADlatel Alexander Duyck napsal: > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index e6f211d..ac60a97 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -5580,6 +5580,7 @@ void *page_frag_alloc_align(struct page_frag_cach= e *nc, > > /* reset page count bias and offset to start of new fra= g */ > > nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; > > offset =3D size - fragsz; > > + BUG_ON(offset < 0); > > } > > > > nc->pagecnt_bias--; > > > > > I think I could be onboard with a patch like this. The test shouldn't > add more than 1 instruction since it is essentially just a jump if > signed test which will be performed after the size - fragsz check. FYI, I hit this problem a few days ago with the nfp network driver, it uses page_frag_alloc() with a frag size larger than PAGE_SIZE when MTU is set to 9000, this may result in memory corruptions when the system runs out of memory. The solution I was working on was something like the following, this makes the allocation fail if fragsz is greater than the cache size. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4dc0d333279f..c6b40b85c55d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5544,12 +5544,17 @@ void *page_frag_alloc_align(struct page_frag_cache = *nc, /* if size can vary use size else just use PAGE_SIZE */ size =3D nc->size; #endif - /* OK, page count is 0, we can safely set it */ - set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); - /* reset page count bias and offset to start of new frag */ nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; offset =3D size - fragsz; + if (unlikely(offset < 0)) { + free_the_page(page, compound_order(page)); + nc->va =3D NULL; + return NULL; + } + + /* OK, page count is 0, we can safely set it */ + set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); } nc->pagecnt_bias--; Maurizio