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From: Nick Desaulniers <ndesaulniers@google.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Joao Moreira <joao@overdrivepizza.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-hardening@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	clang-built-linux <llvm@lists.linux.dev>
Subject: Re: [RFC PATCH v3 07/20] lkdtm: Emit an indirect call for CFI tests
Date: Fri, 10 Jun 2022 16:43:50 -0700	[thread overview]
Message-ID: <CAKwvOd=GRwL6K7GxhiLhRhJVaD3a1VT6MD5fMR4kcYPpd5=0PQ@mail.gmail.com> (raw)
In-Reply-To: <20220610233513.1798771-8-samitolvanen@google.com>

On Fri, Jun 10, 2022 at 4:35 PM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Clang can convert the indirect calls in lkdtm_CFI_FORWARD_PROTO into
> direct calls. Move the call into a noinline function that accepts the
> target address as an argument to ensure the compiler actually emits an
> indirect call instead.

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  drivers/misc/lkdtm/cfi.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c
> index 666a7f4bc137..b6b375112a2a 100644
> --- a/drivers/misc/lkdtm/cfi.c
> +++ b/drivers/misc/lkdtm/cfi.c
> @@ -20,6 +20,13 @@ static noinline int lkdtm_increment_int(int *counter)
>
>         return *counter;
>  }
> +
> +/* Don't allow the compiler to inline the calls. */
> +static noinline void lkdtm_indirect_call(void (*func)(int *))
> +{
> +       func(&called_count);
> +}
> +
>  /*
>   * This tries to call an indirect function with a mismatched prototype.
>   */
> @@ -29,15 +36,11 @@ static void lkdtm_CFI_FORWARD_PROTO(void)
>          * Matches lkdtm_increment_void()'s prototype, but not
>          * lkdtm_increment_int()'s prototype.
>          */
> -       void (*func)(int *);
> -
>         pr_info("Calling matched prototype ...\n");
> -       func = lkdtm_increment_void;
> -       func(&called_count);
> +       lkdtm_indirect_call(lkdtm_increment_void);
>
>         pr_info("Calling mismatched prototype ...\n");
> -       func = (void *)lkdtm_increment_int;
> -       func(&called_count);
> +       lkdtm_indirect_call((void *)lkdtm_increment_int);
>
>         pr_err("FAIL: survived mismatched prototype function call!\n");
>         pr_expected_config(CONFIG_CFI_CLANG);
> --
> 2.36.1.476.g0c4daa206d-goog
>


-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2022-06-10 23:44 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-10 23:34 [RFC PATCH v3 00/20] KCFI support Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 01/20] treewide: Filter out CC_FLAGS_CFI Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 02/20] scripts/kallsyms: Ignore __kcfi_typeid_ Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 03/20] cfi: Remove CONFIG_CFI_CLANG_SHADOW Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 04/20] cfi: Drop __CFI_ADDRESSABLE Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 05/20] cfi: Switch to -fsanitize=kcfi Sami Tolvanen
2022-06-10 23:34 ` [RFC PATCH v3 06/20] cfi: Add type helper macros Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 07/20] lkdtm: Emit an indirect call for CFI tests Sami Tolvanen
2022-06-10 23:43   ` Nick Desaulniers [this message]
2022-06-11  6:01   ` Kees Cook
2022-06-10 23:35 ` [RFC PATCH v3 08/20] arm64: Add types to indirect called assembly functions Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 09/20] arm64: Add CFI error handling Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 10/20] arm64: Drop unneeded __nocfi attributes Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 11/20] init: Drop __nocfi from __init Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 12/20] treewide: Drop function_nocfi Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 13/20] treewide: Drop WARN_ON_FUNCTION_MISMATCH Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 14/20] treewide: Drop __cficanonical Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 15/20] objtool: Disable CFI warnings Sami Tolvanen
2022-06-13 16:10   ` Josh Poimboeuf
2022-06-10 23:35 ` [RFC PATCH v3 16/20] kallsyms: Drop CONFIG_CFI_CLANG workarounds Sami Tolvanen
2022-06-10 23:40   ` Nick Desaulniers
2022-06-13 19:19     ` Bill Wendling
2022-06-10 23:35 ` [RFC PATCH v3 17/20] x86/tools/relocs: Ignore __kcfi_typeid_ relocations Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 18/20] x86: Add types to indirectly called assembly functions Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 19/20] x86/purgatory: Disable CFI Sami Tolvanen
2022-06-10 23:35 ` [RFC PATCH v3 20/20] x86: Add support for CONFIG_CFI_CLANG Sami Tolvanen
2022-07-23 11:21   ` Peter Zijlstra
2022-07-26  0:09     ` Sami Tolvanen
2022-06-13 17:04 ` [RFC PATCH v3 00/20] KCFI support Kees Cook
2022-07-18 21:46   ` Peter Zijlstra
2022-07-19 13:36   ` Will Deacon

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