2022-07-13 22:09:00

by Kees Cook

Subject: [PATCH] x86/alternative: Report missing return thunk details

Debugging missing return thunks is easier if we can see where they're
happening.

Suggested-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
arch/x86/kernel/alternative.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d6858533e6e5..62f6b8b7c4a5 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -555,7 +555,9 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
dest = addr + insn.length + insn.immediate.value;

if (__static_call_fixup(addr, op, dest) ||
- WARN_ON_ONCE(dest != &__x86_return_thunk))
+ WARN_ONCE(dest != &__x86_return_thunk,
+ "missing return thunk: %pS-%pS: %*ph",
+ addr, dest, 5, addr))
continue;

DPRINTK("return thunk at: %pS (%px) len: %d to: %pS",
--
2.32.0

2022-07-14 00:17:33

by Josh Poimboeuf

Subject: Re: [PATCH] x86/alternative: Report missing return thunk details

On Wed, Jul 13, 2022 at 02:38:19PM -0700, Kees Cook wrote:
> Debugging missing return thunks is easier if we can see where they're
> happening.
>
> Suggested-by: Peter Zijlstra <[email protected]>
> Link: https://lore.kernel.org/lkml/[email protected]/
> Cc: Peter Zijlstra <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
> arch/x86/kernel/alternative.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index d6858533e6e5..62f6b8b7c4a5 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -555,7 +555,9 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
> dest = addr + insn.length + insn.immediate.value;
>
> if (__static_call_fixup(addr, op, dest) ||
> - WARN_ON_ONCE(dest != &__x86_return_thunk))
> + WARN_ONCE(dest != &__x86_return_thunk,
> + "missing return thunk: %pS-%pS: %*ph",
> + addr, dest, 5, addr))

String needs a newline?

--
Josh