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(dmkd798g-7z2-yccwcp-4.rev.dnainternet.fi. [2001:14bb:52:7be:f0bf:dd2d:f008:5213]) by smtp.gmail.com with ESMTPSA id r22-v6sm2041418ljh.77.2018.10.29.13.01.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Oct 2018 13:01:24 -0700 (PDT) Subject: Re: [PATCH 02/17] prmem: write rare for static allocation To: Peter Zijlstra Cc: Mimi Zohar , Kees Cook , Matthew Wilcox , Dave Chinner , James Morris , Michal Hocko , kernel-hardening@lists.openwall.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, igor.stoppa@huawei.com, Dave Hansen , Jonathan Corbet , Laura Abbott , Vlastimil Babka , "Kirill A. Shutemov" , Andrew Morton , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20181023213504.28905-1-igor.stoppa@huawei.com> <20181023213504.28905-3-igor.stoppa@huawei.com> <20181026094105.GE3159@worktop.c.hoisthospitality.com> From: Igor Stoppa Message-ID: Date: Mon, 29 Oct 2018 22:01:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181026094105.GE3159@worktop.c.hoisthospitality.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/10/2018 10:41, Peter Zijlstra wrote: > On Wed, Oct 24, 2018 at 12:34:49AM +0300, Igor Stoppa wrote: >> +static __always_inline > > That's far too large for inline. The reason for it is that it's supposed to minimize the presence of gadgets that might be used in JOP attacks. I am ready to stand corrected, if I'm wrong, but this is the reason why I did it. Regarding the function being too large, yes, I would not normally choose it for inlining. Actually, I would not normally use "__always_inline" and instead I would limit myself to plain "inline", at most. > >> +bool wr_memset(const void *dst, const int c, size_t n_bytes) >> +{ >> + size_t size; >> + unsigned long flags; >> + uintptr_t d = (uintptr_t)dst; >> + >> + if (WARN(!__is_wr_after_init(dst, n_bytes), WR_ERR_RANGE_MSG)) >> + return false; >> + while (n_bytes) { >> + struct page *page; >> + uintptr_t base; >> + uintptr_t offset; >> + uintptr_t offset_complement; >> + >> + local_irq_save(flags); >> + page = virt_to_page(d); >> + offset = d & ~PAGE_MASK; >> + offset_complement = PAGE_SIZE - offset; >> + size = min(n_bytes, offset_complement); >> + base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL); >> + if (WARN(!base, WR_ERR_PAGE_MSG)) { >> + local_irq_restore(flags); >> + return false; >> + } >> + memset((void *)(base + offset), c, size); >> + vunmap((void *)base); > > BUG yes, somehow I managed to drop this debug configuration from the debug builds I made. [...] > Also, I see an amount of duplication here that shows you're not nearly > lazy enough. I did notice a certain amount of duplication, but I didn't know how to exploit it. -- igor