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Mon, 9 Mar 2020 09:12:07 +0000 (GMT) Subject: Re: [PATCH] mm: mmap: show vm_unmapped_area error log To: Matthew Wilcox Cc: Andrew Morton , walken@google.com, bp@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com From: Jaewon Kim Message-ID: <5E660863.2090104@samsung.com> Date: Mon, 9 Mar 2020 18:12:03 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <20200308123616.GH31215@bombadil.infradead.org> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrEJsWRmVeSWpSXmKPExsWy7bCmrm4GR1qcwepNKhZz1q9hs5jYr2nR vXkmo8XlXXPYLO6t+c9q8W9SrcXvH3PYHNg9ds66y+6xYFOpx+YVWh6bPk1i9zgx4zeLx+bT 1R6fN8kFsEfl2GSkJqakFimk5iXnp2TmpdsqeQfHO8ebmhkY6hpaWpgrKeQl5qbaKrn4BOi6 ZeYA3aKkUJaYUwoUCkgsLlbSt7Mpyi8tSVXIyC8usVVKLUjJKTA0KNArTswtLs1L10vOz7Uy NDAwMgWqTMjJeHNtOVPBdfGKFd1T2BsYrwh1MXJySAiYSEyZ9Yixi5GLQ0hgB6NEb/MdFgjn E6PE+02bWSGcb4wSyzva2GBaFu3cBNWyl1Fi9aeP7BDOW0aJ1mPXWECqhAXsJI5NPQLUzsEh IqAh8WaLEUgNs8AsRol93YeYQWrYBLQl3i+YxApi8wpoSTxtW8MEYrMIqEis+jmJEcQWFYiQ 2DH3IyNEjaDEyZlPwOZzCthInDixkR3EZhaQl2jeOpsZZIGEwH02iZsP5jFBnOoi8fNmEwuE LSzx6vgWdghbSuJlfxs7REMzo8TbmZsZIZwWRom7m3oZIaqMJXp7LjCDvMAsoCmxfpc+RFhR YufvuYwQm/kk3n3tAftSQoBXoqMNGqpqEi3PvrJC2DISf/89g7I9JHZsPsUGCa2bzBJPD79i msCoMAvJc7OQPDQLYfMCRuZVjGKpBcW56anFhgXGyJG8iRGcPrXMdzBuOOdziFGAg1GJh/eB fGqcEGtiWXFl7iFGCQ5mJRHeRq3kOCHelMTKqtSi/Pii0pzU4kOMpsDwnsgsJZqcD0zteSXx hqZGxsbGFiZm5mamxkrivA8jNeOEBNITS1KzU1MLUotg+pg4OKUaGGPvT59VG3VYzcVs07VN j552xBeHed2csPLltuoQWU691b/XTW9awerib3rm0GzX03It1X0/TvZ1PFPZ0rHG9kz2Qr7p C9R0/rl/brvJWXeh8bdhwArPVV/8p3U9CU6eFMmeqJz1XVkiNWBPTUXNraiNCy6wHy7WNLug f8WM9fPhoOeH5xX9n67EUpyRaKjFXFScCABGE4/WtQMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrPLMWRmVeSWpSXmKPExsWy7bCSvG4GR1qcweyrbBZz1q9hs5jYr2nR vXkmo8XlXXPYLO6t+c9q8W9SrcXvH3PYHNg9ds66y+6xYFOpx+YVWh6bPk1i9zgx4zeLx+bT 1R6fN8kFsEdx2aSk5mSWpRbp2yVwZby5tpyp4Lp4xYruKewNjFeEuhg5OSQETCQW7dzE2MXI xSEksJtR4uqJH2wQCRmJN+efsnQxcgDZwhKHDxeDhIUEXjNKzLjFAWILC9hJHJt6hBWkRERA Q+LNFiOIMTeZJWY1fWAHqWEWmMEocWShM4jNJqAt8X7BJFYQm1dAS+Jp2xomEJtFQEVi1c9J jCC2qECExOp115ghagQlTs58wgJicwrYSJw4sRFqprrEn3mXmCFseYnmrbOZJzAKzkLSMgtJ 2SwkZQsYmVcxSqYWFOem5xYbFhjlpZbrFSfmFpfmpesl5+duYgRHg5bWDsYTJ+IPMQpwMCrx 8D6QT40TYk0sK67MPcQowcGsJMLbqJUcJ8SbklhZlVqUH19UmpNafIhRmoNFSZxXPv9YpJBA emJJanZqakFqEUyWiYNTqoHReMuCQyHH1DcVHkl9/39rs1aJ0JGEG7026iJpb/hkt854w+D0 vj8r+77qrkaWd3vVL+7bpbbr4M8F2alHVOzkZz336Y9nY92kM1davspBzkjvx9YFCRWVoV4L eIRyvgeGbr591tpC+yl7VN6CmBkNvHOSXK+WHN2udIlxtexuhYQFRV/TX6krsRRnJBpqMRcV JwIAoCF464ICAAA= X-CMS-MailID: 20200309091208epcas1p30087f3874f2fe6f3399c026ec93d631b X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-Sendblock-Type: SVC_REQ_APPROVE CMS-TYPE: 101P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20200304030211epcas1p4da8cb569947aefb3aad1da039aaabce4 References: <20200304030206.1706-1-jaewon31.kim@samsung.com> <5E605749.9050509@samsung.com> <20200305202443.8de3598558336b1d75afbba7@linux-foundation.org> <5E61EAB6.5080609@samsung.com> <20200307154744.acd523831b45efa8d0fc1dfa@linux-foundation.org> <20200308015802.GD31215@bombadil.infradead.org> <5E64C1D7.3000208@samsung.com> <20200308123616.GH31215@bombadil.infradead.org> Content-Transfer-Encoding: quoted-printable 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 2020=EB=85=84 03=EC=9B=94 08=EC=9D=BC 21:36, Matthew Wilcox wrote: > On Sun, Mar 08, 2020 at 06:58:47PM +0900, Jaewon Kim wrote: >> On 2020=EB=85=84 03=EC=9B=94 08=EC=9D=BC 10:58, Matthew Wilcox wrote: >>> On Sat, Mar 07, 2020 at 03:47:44PM -0800, Andrew Morton wrote: >>>> On Fri, 6 Mar 2020 15:16:22 +0900 Jaewon Kim wrote: >>>>> Even on 64 bit kernel, the mmap failure can happen for a 32 bit tas= k. >>>>> Virtual memory space shortage of a task on mmap is reported to user= space >>>>> as -ENOMEM. It can be confused as physical memory shortage of overa= ll >>>>> system. >>> But userspace can trigger this printk. We don't usually allow printk= s >>> under those circumstances, even ratelimited. >> Hello thank you your comment. >> >> Yes, userspace can trigger printk, but this was useful for to know why >> a userspace task was crashed. There seems to be still many userspace >> applications which did not check error of mmap and access invalid addr= ess. >> >> Additionally in my AARCH64 Android environment, display driver tries t= o >> get userspace address to map its display memory. The display driver >> report -ENOMEM from vm_unmapped_area and but also from GPU related >> address space. >> >> Please let me know your comment again if this debug is now allowed >> in that userspace triggered perspective. > The scenario that worries us is an attacker being able to fill the log > files and so also fill (eg) the /var partition. Once it's full, future > kernel messages cannot be stored anywhere and so there will be no trace= s > of their privilege escalation. Although up to 10 times within 5 secs is not many, I think those log may = remove other important log in log buffer if it is the system which produces very= few log. In my Android phone device system, there seems to be much more kernel log= though. > Maybe a tracepoint would be a better idea? Usually they are disabled, > but they can be enabled by a sysadmin to gain insight into why an > application is crashing. In Android phone device system, we cannot get sysadmin permission if it i= s built for end user. And it is not easy to reproduce this symptom because it is = an user's app. Anyway let me try pr_devel_ratelimited which is disabled by default. I ho= pe this is good enough. Additionally I moved the code from mm.h to mmap.c. --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2069,7 +2069,7 @@ unsigned long vm_unmapped_area(struct vm_unmapped_a= rea_info *info) addr =3D unmapped_area(info); =20 if (IS_ERR_VALUE(addr)) { - pr_warn_ratelimited("%s err:%ld total_vm:0x%lx flags:0x%l= x len:0x%lx low:0x%lx high:0x%lx mask:0x%lx offset:0x%lx\n", + pr_devel_ratelimited("%s err:%ld total_vm:0x%lx flags:0x%= lx len:0x%lx low:0x%lx high:0x%lx mask:0x%lx offset:0x%lx\n", __func__, addr, current->mm->total_vm, info->flag= s, info->length, info->low_limit, info->high_limit, info->align_mask, info->align_offset); > >