linux-kernel - [PATCH] gcc-plugins/stackleak: Use noinstr in favor of notrace

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Date:   Tue,  1 Feb 2022 16:19:18 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] gcc-plugins/stackleak: Use noinstr in favor of notrace

While the stackleak plugin was already using notrace, objtool is now a
bit more picky. Update the notrace uses to noinstr. Silences these
warnings:

vmlinux.o: warning: objtool: do_syscall_64()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_int80_syscall_32()+0x9: call to stackleak_track_stack() leaves .noinstr.text section
vmlinux.o: warning: objtool: exc_general_protection()+0x22: call to stackleak_track_stack() leaves .noinstr.text section
vmlinux.o: warning: objtool: fixup_bad_iret()+0x20: call to stackleak_track_stack() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_machine_check()+0x27: call to stackleak_track_stack() leaves .noinstr.text section
vmlinux.o: warning: objtool: .text+0x5346e: call to stackleak_erase() leaves .noinstr.text section
vmlinux.o: warning: objtool: .entry.text+0x143: call to stackleak_erase() leaves .noinstr.text section
vmlinux.o: warning: objtool: .entry.text+0x10eb: call to stackleak_erase() leaves .noinstr.text section
vmlinux.o: warning: objtool: .entry.text+0x17f9: call to stackleak_erase() leaves .noinstr.text section

Cc: Alexander Popov <alex.popov@...ux.com>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/lkml/YYENAKB0igNFnFmK@hirez.programming.kicks-ass.net/
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Is it correct to exclude .noinstr.text here? That means any functions called in
there will have their stack utilization untracked. This doesn't seem right to me,
though. Shouldn't stackleak_track_stack() just be marked noinstr instead?
---
 kernel/stackleak.c                     | 3 +--
 scripts/gcc-plugins/stackleak_plugin.c | 3 +++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index 66b8af394e58..72d4ebf49480 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -70,7 +70,7 @@ late_initcall(stackleak_sysctls_init);
 #define skip_erasing()	false
 #endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
 
-asmlinkage void notrace stackleak_erase(void)
+asmlinkage void noinstr stackleak_erase(void)
 {
 	/* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
 	unsigned long kstack_ptr = current->lowest_stack;
@@ -124,7 +124,6 @@ asmlinkage void notrace stackleak_erase(void)
 	/* Reset the 'lowest_stack' value for the next syscall */
 	current->lowest_stack = current_top_of_stack() - THREAD_SIZE/64;
 }
-NOKPROBE_SYMBOL(stackleak_erase);
 
 void __used __no_caller_saved_registers notrace stackleak_track_stack(void)
 {
diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
index e9db7dcb3e5f..e7e51f0eb597 100644
--- a/scripts/gcc-plugins/stackleak_plugin.c
+++ b/scripts/gcc-plugins/stackleak_plugin.c
@@ -429,6 +429,7 @@ static unsigned int stackleak_cleanup_execute(void)
 	return 0;
 }
 
+/* Do not instrument anything found in special sections. */
 static bool stackleak_gate(void)
 {
 	tree section;
@@ -446,6 +447,8 @@ static bool stackleak_gate(void)
 			return false;
 		if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13))
 			return false;
+		if (!strncmp(TREE_STRING_POINTER(section), ".noinstr.text", 13))
+			return false;
 	}
 
 	return track_frame_size >= 0;
-- 
2.30.2