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imf06.hostedemail.com; dkim=pass header.d=meta.com header.s=s2048-2021-q4 header.b=nql86g6A; spf=pass (imf06.hostedemail.com: domain of "prvs=129037c652=songliubraving@meta.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=129037c652=songliubraving@meta.com"; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=reject) header.from=meta.com ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1666105554; a=rsa-sha256; cv=pass; b=j3+mrXHCxqOGf3JQrT5LYscRceYh3WsVv0/qcQhh1iAv1lrKRgWR+bWJdvOPBjeTI0aEfD gmCKBd1WUX413hxAhzZZEQfzeYcQHqRyQM5f+rikxIUh7AUf9MjGV0EDO8TNuohxP9V3pr VJybw8hBTx8pNkmaXxmSpnwulSvLsSE= ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666105554; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ERPLGJTG6pwg/kqG9LAnpSZp7NdEA+VN9Sb9XyKj1ac=; b=hddVB+gpwmFBuA/nE7vruvypUrYQ2tL3SfUgNFw3Qyll809SszKRKR1aP+Uo1ZZl0IF9Cy LeTbIqMUKyQnnc4HdbxRvCt0hFA2V7Zxfw1Lh+mkArWn/nI+8o0HLEFGnlPiaKSV5HkC1z DTUiHbA2M+NK4i61rLMI8AwWlxIPnBE= X-Stat-Signature: kcpsxqtt878uocqwmdzzfx36poccs65p X-Rspamd-Queue-Id: 48FB2180046 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=meta.com header.s=s2048-2021-q4 header.b=nql86g6A; spf=pass (imf06.hostedemail.com: domain of "prvs=129037c652=songliubraving@meta.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=129037c652=songliubraving@meta.com"; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=reject) header.from=meta.com X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1666105554-376795 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 Oct 18, 2022, at 7:50 AM, Christoph Hellwig wrote: >=20 > On Mon, Oct 17, 2022 at 04:23:52PM +0000, Song Liu wrote: >>> Well, nothing explains what the method is to avoid having memory >>> that is mapped writable and executable at the same time, which really >>> could use some explanation here (and in the main patch as well). >>=20 >> Thanks for the feedback. I will add this.=20 >>=20 >> Does the code look good to you? I personally think patch 1, 2, 4 could >> ship with a little more work.=20 >=20 > I only took a quick look and I'm not sure how the W^X actually works. > Yes, it alls into the text poke helpers, but how do these work on > less than page sized allocations? Aha, I guess I understand your point (and concern) now.=20 It is the same as text poke into static kernel text: we create a local=20 writable mapping to the memory we need to update. For less than page sized allocation, this mapping does have access to X memory that may=20 belong to a different allocation, just like text poke into static=20 kernel text.=20 Maybe we need something like vcopy_exec(x_mem, tmp_buf, size), where we explicitly check the allowed memory of x_mem is bigger or equal to size. And users of vmalloc_exec should only use vcopy_exec to update memory from vmalloc_exec.=20 Does this make sense? Did I understand your concern correctly?=20 Thanks, Song