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[209.85.220.65]) by mx.google.com with SMTPS id 17sor33209253itl.16.2019.04.25.13.44.08 for (Google Transport Security); Thu, 25 Apr 2019 13:44:08 -0700 (PDT) Received-SPF: pass (google.com: domain of matthewgarrett@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=X2Y0UXdY; spf=pass (google.com: domain of matthewgarrett@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=matthewgarrett@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=9T6Hh/gfaAIMuibwKFS2lWem2Wt7fkhHXq9vbgpXfiI=; b=X2Y0UXdYtsf1r8qUOurjsJI9eewtbXZBIc9FX3ykI64j+N6JDnvmPQgxohph6tOAzh 7oT8+8CwhPf9xiD3Jz16lMZwg6HYfEE8hmUoI3+5Q24DAvTT3LMS318fjKrafBTKMLdp /QCm5H30eeFrFQyoJqAQU6mLKhoOiFOFRKOys6WzC7PITt6PGmRIb68eV+Q9vbOIF8Lp dqqIBIsuqZsLmIJYgH7ifXN/C6bkykkP+VnH630efhebTaBgEkxtI5L/ops1ha0ExfBP J1iXAkZ/9AP474L4907G3yTct2zTI6Gj5ZWvtNVMWWSZmkuBm4Tepf10tdXxOFJ9VNkb ZKGA== X-Google-Smtp-Source: APXvYqxUbgSe5G0v+X+ayIdnr1/C14jU5CTpxKyeEQxe4lKH3qBoI0CAJN7yD+zzO60X6w4ddn4L7c2JaoYQn+CBs54= X-Received: by 2002:a24:eb04:: with SMTP id h4mr3421463itj.16.1556225048269; Thu, 25 Apr 2019 13:44:08 -0700 (PDT) MIME-Version: 1.0 References: <20190424211038.204001-1-matthewgarrett@google.com> <20190425121410.GC1144@dhcp22.suse.cz> In-Reply-To: From: Matthew Garrett Date: Thu, 25 Apr 2019 13:43:57 -0700 Message-ID: Subject: Re: [PATCH V2] mm: Allow userland to request that the kernel clear memory on release To: Jann Horn Cc: Michal Hocko , Linux-MM , kernel list , Linux API Content-Type: text/plain; charset="UTF-8" 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: On Thu, Apr 25, 2019 at 5:43 AM Jann Horn wrote: > An interesting effect of this is that it will be possible to set this > on a CoW anon VMA in a fork() child, and then the semantics in the > parent will be subtly different - e.g. if the parent vmsplice()d a > CoWed page into a pipe, then forked an unprivileged child, the child > set MADV_WIPEONRELEASE on its VMA, the parent died somehow, and then > the child died, the page in the pipe would be zeroed out. A child > should not be able to affect its parent like this, I think. If this > was an mmap() flag instead of a madvise() command, that issue could be > avoided. Alternatively, if adding more mmap() flags doesn't work, > perhaps you could scan the VMA and ensure that it contains no pages > yet, or something like that? I /think/ my argument here would be not to do that? I agree that it's unexpected, but I guess the other alternative would be to force a copy on any existing COW pages in the VMA at madvise() time, and maybe also at fork() time (sort of like the behaviour of MADV_WIPEONFORK, but copying the page rather than providing a new zero page) > I think all the callers have a reference to the VMA, so perhaps you > could add a VMA parameter to page_remove_rmap() and then look at the > VMA in there? I'll dig into that, thanks!