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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:52960) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kYXem-0006Ot-8l; Fri, 30 Oct 2020 16:53:40 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1kYXel-0007KL-3L; Fri, 30 Oct 2020 16:53:39 +0000 Date: Fri, 30 Oct 2020 16:53:39 +0000 From: Russell King - ARM Linux admin To: Arnd Bergmann Subject: Re: [PATCH 4/9] ARM: syscall: always store thread_info->syscall Message-ID: <20201030165338.GG1551@shell.armlinux.org.uk> References: <20201030154519.1245983-1-arnd@kernel.org> <20201030154919.1246645-1-arnd@kernel.org> <20201030154919.1246645-4-arnd@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201030154919.1246645-4-arnd@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201030_125648_077958_E057EFF5 X-CRM114-Status: GOOD ( 17.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, arnd@arndb.de, linus.walleij@linaro.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, viro@zeniv.linux.org.uk, Christoph Hellwig , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Oct 30, 2020 at 04:49:14PM +0100, Arnd Bergmann wrote: > From: Arnd Bergmann > > The system call number is used in a a couple of places, in particular > ptrace, seccomp and /proc//syscall. > > The last one apparently never worked reliably on ARM for tasks > that are not currently getting traced. > > Storing the syscall number in the normal entry path makes it work, > as well as allowing us to see if the current system call is for > OABI compat mode, which is the next thing I want to hook into. I'm not sure this patch is correct. Tracing the existing code for OABI: asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) { current_thread_info()->syscall = scno; /* Legacy ABI only. */ USER( ldr scno, [saved_pc, #-4] ) @ get SWI instruction bic scno, scno, #0xff000000 @ mask off SWI op-code eor scno, scno, #__NR_SYSCALL_BASE @ check OS number tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? bne __sys_trace __sys_trace: mov r1, scno add r0, sp, #S_OFF bl syscall_trace_enter So, thread_info->syscall does not include __NR_SYSCALL_BASE. The reason for this is the code that makes use of that via syscall_get_nr(). kernel/trace/trace_syscalls.c: syscall_nr = trace_get_syscall_nr(current, regs); if (syscall_nr < 0 || syscall_nr >= NR_syscalls) return; and NR_syscalls is the number of syscalls, which doesn't include the __NR_SYSCALL_BASE offset. So, I think this patch actually breaks OABI. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel