Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 16 Apr 2021 13:38:43 -0700
In-Reply-To: <20210416203844.3803177-1-samitolvanen@google.com>
Message-Id: <20210416203844.3803177-15-samitolvanen@google.com>
Mime-Version: 1.0
References: <20210416203844.3803177-1-samitolvanen@google.com>
Subject: [PATCH 14/15] x86, kprobes: Fix optprobe_template_func type mismatch
From:   Sami Tolvanen <samitolvanen@google.com>
To:     x86@kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Sami Tolvanen <samitolvanen@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

The optprobe_template_func symbol is defined in inline assembly,
but it's not marked global, which conflicts with the C declaration
needed for STACK_FRAME_NON_STANDARD and confuses the compiler when
CONFIG_CFI_CLANG is enabled.

Marking the symbol global would make the compiler happy, but as the
compiler also generates a CFI jump table entry for all address-taken
functions, the jump table ends up containing a jump to the .rodata
section where optprobe_template_func resides, which results in an
objtool warning.

Use ASM_STACK_FRAME_NON_STANDARD instead to avoid both issues.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/x86/kernel/kprobes/opt.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 71425ebba98a..95375ef5deee 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -103,6 +103,7 @@ static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
 asm (
 			".pushsection .rodata\n"
 			"optprobe_template_func:\n"
+			ASM_STACK_FRAME_NON_STANDARD(optprobe_template_func)
 			".global optprobe_template_entry\n"
 			"optprobe_template_entry:\n"
 #ifdef CONFIG_X86_64
@@ -154,9 +155,6 @@ asm (
 			"optprobe_template_end:\n"
 			".popsection\n");
 
-void optprobe_template_func(void);
-STACK_FRAME_NON_STANDARD(optprobe_template_func);
-
 #define TMPL_CLAC_IDX \
 	((long)optprobe_template_clac - (long)optprobe_template_entry)
 #define TMPL_MOVE_IDX \
-- 
2.31.1.368.gbe11c130af-goog