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Venkataraman" To: Mark Brown Cc: jpoimboe@redhat.com, mark.rutland@arm.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <65cf4dfbc439b010b50a0c46ec500432acde86d6> <20210503173615.21576-1-madvenka@linux.microsoft.com> <20210503173615.21576-3-madvenka@linux.microsoft.com> <20210504160508.GC7094@sirena.org.uk> <1bd2b177-509a-21d9-e349-9b2388db45eb@linux.microsoft.com> Message-ID: <0f72c4cb-25ef-ee23-49e4-986542be8673@linux.microsoft.com> Date: Tue, 4 May 2021 14:32:35 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <1bd2b177-509a-21d9-e349-9b2388db45eb@linux.microsoft.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210504_123237_564659_3EDAABF2 X-CRM114-Status: GOOD ( 33.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 5/4/21 2:03 PM, Madhavan T. Venkataraman wrote: > > > On 5/4/21 11:05 AM, Mark Brown wrote: >> On Mon, May 03, 2021 at 12:36:13PM -0500, madvenka@linux.microsoft.com wrote: >>> From: "Madhavan T. Venkataraman" >>> >>> Create a sym_code_ranges[] array to cover the following text sections that >>> contain functions defined as SYM_CODE_*(). These functions are low-level >> >> This makes sense to me - a few of bikesheddy comments below but nothing >> really substantive. >> > > OK. > >>> +static struct code_range *lookup_range(unsigned long pc) >> >> This feels like it should have a prefix on the name (eg, unwinder_) >> since it looks collision prone. Or lookup_code_range() rather than just >> plain lookup_range(). >> > > I will add the prefix. > >>> +{ >> + struct code_range *range; >> + >> + for (range = sym_code_ranges; range->start; range++) { >> >> It seems more idiomatic to use ARRAY_SIZE() rather than a sentinel here, >> the array can't be empty. >> > > If there is a match, I return the matched range. Else, I return the sentinel. > This is just so I don't have to check for range == NULL after calling > lookup_range(). > > I will change it to what you have suggested and check for NULL explicitly. > It is not a problem. > >>> + range = lookup_range(frame->pc); >>> + >>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER >>> if (tsk->ret_stack && >>> frame->pc == (unsigned long)return_to_handler) { >>> @@ -118,9 +160,21 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) >>> return -EINVAL; >>> frame->pc = ret_stack->ret; >>> frame->pc = ptrauth_strip_insn_pac(frame->pc); >>> + return 0; >>> } >> >> Do we not need to look up the range of the restored pc and validate >> what's being pointed to here? It's not immediately obvious why we do >> the lookup before handling the function graph tracer, especially given >> that we never look at the result and there's now a return added skipping >> further reliability checks. At the very least I think this needs some >> additional comments so the code is more obvious. > I want sym_code_ranges[] to contain both unwindable and non-unwindable ranges. > Unwindable ranges will be special ranges such as the return_to_handler() and > kretprobe_trampoline() functions for which the unwinder has (or will have) > special code to unwind. So, the lookup_range() has to happen before the > function graph code. Please look at the last patch in the series for > the fix for the above function graph code. > > On the question of "should the original return address be checked against > sym_code_ranges[]?" - I assumed that if there is a function graph trace on a > function, it had to be an ftraceable function. It would not be a part > of sym_code_ranges[]. Is that a wrong assumption on my part? > If you prefer, I could do something like this: check_pc: if (!__kernel_text_address(frame->pc)) frame->reliable = false; range = lookup_range(frame->pc); #ifdef CONFIG_FUNCTION_GRAPH_TRACER if (tsk->ret_stack && frame->pc == (unsigned long)return_to_handler) { ... frame->pc = ret_stack->ret; frame->pc = ptrauth_strip_insn_pac(frame->pc); goto check_pc; } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ Is that acceptable? Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel