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[213.175.37.12]) by smtp.gmail.com with ESMTPSA id q7sm1884016wrs.73.2021.10.08.02.13.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Oct 2021 02:13:49 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa To: "Steven Rostedt (VMware)" Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Subject: [PATCH 2/8] x86/ftrace: Remove fault protection code in prepare_ftrace_return Date: Fri, 8 Oct 2021 11:13:30 +0200 Message-Id: <20211008091336.33616-3-jolsa@kernel.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20211008091336.33616-1-jolsa@kernel.org> References: <20211008091336.33616-1-jolsa@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (VMware)" Removing the fault protection code when writing return_hooker to stack. As Steven noted: > That protection was there from the beginning due to being "paranoid", > considering ftrace was bricking network cards. But that protection > would not have even protected against that. Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Jiri Olsa --- arch/x86/kernel/ftrace.c | 38 +++----------------------------------- 1 file changed, 3 insertions(+), 35 deletions(-) diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 1b3ce3b4a2a2..c555624da989 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -625,12 +625,10 @@ int ftrace_disable_ftrace_graph_caller(void) * Hook the return address and push it in the stack of return addrs * in current thread info. */ -void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, +void prepare_ftrace_return(unsigned long ip, unsigned long *parent, unsigned long frame_pointer) { unsigned long return_hooker = (unsigned long)&return_to_handler; - unsigned long old; - int faulted; /* * When resuming from suspend-to-ram, this function can be indirectly @@ -650,37 +648,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, if (unlikely(atomic_read(¤t->tracing_graph_pause))) return; - /* - * Protect against fault, even if it shouldn't - * happen. This tool is too much intrusive to - * ignore such a protection. - */ - asm volatile( - "1: " _ASM_MOV " (%[parent]), %[old]\n" - "2: " _ASM_MOV " %[return_hooker], (%[parent])\n" - " movl $0, %[faulted]\n" - "3:\n" - - ".section .fixup, \"ax\"\n" - "4: movl $1, %[faulted]\n" - " jmp 3b\n" - ".previous\n" - - _ASM_EXTABLE(1b, 4b) - _ASM_EXTABLE(2b, 4b) - - : [old] "=&r" (old), [faulted] "=r" (faulted) - : [parent] "r" (parent), [return_hooker] "r" (return_hooker) - : "memory" - ); - - if (unlikely(faulted)) { - ftrace_graph_stop(); - WARN_ON(1); - return; - } - - if (function_graph_enter(old, self_addr, frame_pointer, parent)) - *parent = old; + if (!function_graph_enter(*parent, ip, frame_pointer, parent)) + *parent = return_hooker; } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ -- 2.31.1