* [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace
@ 2022-02-03 20:17 Kees Cook
2022-02-04 1:14 ` Linus Torvalds
2022-02-06 12:35 ` Peter Zijlstra
0 siblings, 2 replies; 4+ messages in thread
From: Kees Cook @ 2022-02-03 20:17 UTC (permalink / raw)
To: Alexander Popov
Cc: Kees Cook, Peter Zijlstra, Linus Torvalds, Thomas Gleixner,
Josh Poimboeuf, Borislav Petkov, linux-kernel, linux-hardening
While the stackleak plugin was already using notrace, objtool is now a
bit more picky. Update the notrace uses to noinstr. Silences the
following objtool warnings when building with:
CONFIG_DEBUG_ENTRY=y
CONFIG_STACK_VALIDATION=y
CONFIG_VMLINUX_VALIDATION=y
CONFIG_GCC_PLUGIN_STACKLEAK=y
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
Note that the plugin's addition of calls to stackleak_track_stack()
from noinstr functions is expected to be safe, as it isn't runtime
instrumentation and is self-contained.
Cc: Alexander Popov <alex.popov@linux.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
kernel/stackleak.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index 66b8af394e58..ddb5a7f48d69 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;
@@ -124,9 +124,8 @@ 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)
+void __used __no_caller_saved_registers noinstr stackleak_track_stack(void)
{
unsigned long sp = current_stack_pointer;
--
2.30.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace
2022-02-03 20:17 [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace Kees Cook
@ 2022-02-04 1:14 ` Linus Torvalds
2022-02-04 8:03 ` Borislav Petkov
2022-02-06 12:35 ` Peter Zijlstra
1 sibling, 1 reply; 4+ messages in thread
From: Linus Torvalds @ 2022-02-04 1:14 UTC (permalink / raw)
To: Kees Cook
Cc: Alexander Popov, Peter Zijlstra, Thomas Gleixner, Josh Poimboeuf,
Borislav Petkov, Linux Kernel Mailing List, linux-hardening
On Thu, Feb 3, 2022 at 12:18 PM Kees Cook <keescook@chromium.org> wrote:
>
> While the stackleak plugin was already using notrace, objtool is now a
> bit more picky. Update the notrace uses to noinstr. Silences the
> following objtool warnings when building with:
Thanks, applied.
There are still a few objtool warnings about other issues, all look
somehow related to mce:
mce_start()+0x5c: call to __kasan_check_write() leaves .noinstr.text section
mce_gather_info()+0x5f: call to v8086_mode.constprop.0() leaves
.noinstr.text section
mce_read_aux()+0x8a: call to mca_msr_reg() leaves .noinstr.text section
do_machine_check()+0x197: call to mce_no_way_out() leaves
.noinstr.text section
mce_severity_amd.constprop.0()+0xca: call to mce_severity_amd_smca()
leaves .noinstr.textp section
and from a quick look at least some of them look like real bugs.
For example, mce_read_aux() is marked 'noinstr', but it calls
mca_msr_reg() which is not. That's iffy.
The others might be compiler-generated (the 'constprop' thing has
caused section issues before so I didn't bother looking closer). Or
related to kasan. But at least one of them seems to be a valid warning
about bad behavior.
Linus
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace
2022-02-04 1:14 ` Linus Torvalds
@ 2022-02-04 8:03 ` Borislav Petkov
0 siblings, 0 replies; 4+ messages in thread
From: Borislav Petkov @ 2022-02-04 8:03 UTC (permalink / raw)
To: Linus Torvalds
Cc: Kees Cook, Alexander Popov, Peter Zijlstra, Thomas Gleixner,
Josh Poimboeuf, Linux Kernel Mailing List, linux-hardening
On Thu, Feb 03, 2022 at 05:14:11PM -0800, Linus Torvalds wrote:
> There are still a few objtool warnings about other issues, all look
> somehow related to mce:
I have a small patchset addressing that, ofc. It is on its way to be
sent out but there's always something else preempting me... :-\
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace
2022-02-03 20:17 [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace Kees Cook
2022-02-04 1:14 ` Linus Torvalds
@ 2022-02-06 12:35 ` Peter Zijlstra
1 sibling, 0 replies; 4+ messages in thread
From: Peter Zijlstra @ 2022-02-06 12:35 UTC (permalink / raw)
To: Kees Cook
Cc: Alexander Popov, Linus Torvalds, Thomas Gleixner, Josh Poimboeuf,
Borislav Petkov, linux-kernel, linux-hardening
On Thu, Feb 03, 2022 at 12:17:54PM -0800, Kees Cook wrote:
> While the stackleak plugin was already using notrace, objtool is now a
> bit more picky. Update the notrace uses to noinstr. Silences the
> following objtool warnings when building with:
>
> CONFIG_DEBUG_ENTRY=y
> CONFIG_STACK_VALIDATION=y
> CONFIG_VMLINUX_VALIDATION=y
> CONFIG_GCC_PLUGIN_STACKLEAK=y
>
> 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
>
> Note that the plugin's addition of calls to stackleak_track_stack()
> from noinstr functions is expected to be safe, as it isn't runtime
> instrumentation and is self-contained.
>
> Cc: Alexander Popov <alex.popov@linux.com>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
No, I didn't suggest this and it is actively wrong. noinstr *really*
should mean no instrumentation, nothing, nada, zip.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-02-03 20:17 [PATCH v2] gcc-plugins/stackleak: Use noinstr in favor of notrace Kees Cook
2022-02-04 1:14 ` Linus Torvalds
2022-02-04 8:03 ` Borislav Petkov
2022-02-06 12:35 ` Peter Zijlstra
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