From: Nick Desaulniers <ndesaulniers@google.com>
To: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc: jeyu@kernel.org, keescook@chromium.org, nathan@kernel.org,
samitolvanen@google.com, Miroslav Benes <mbenes@suse.cz>,
Stephen Boyd <swboyd@chromium.org>, Joe Perches <joe@perches.com>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
Fangrui Song <maskray@google.com>
Subject: Re: [PATCH v5] kallsyms: strip CLANG CFI postfix ".cfi_jt"
Date: Fri, 1 Oct 2021 11:29:45 -0700 [thread overview]
Message-ID: <CAKwvOdmXtTE15mUb5x7Lq==emFwba7OGLfx9skayP-G9NqeiNQ@mail.gmail.com> (raw)
In-Reply-To: <20210814124224.8551-1-treasure4paddy@gmail.com>
On Sat, Aug 14, 2021 at 5:43 AM Padmanabha Srinivasaiah
<treasure4paddy@gmail.com> wrote:
>
> Clang CFI adds a postfix ".cfi_jt" to a symbols of extern functions.
> For e.g. this breaks syscall tracer that doesn't expect such postfix,
> so strip out the postfix from the expanded symbol.
$ llvm-nm vmlinux | grep -e 'T ' -e 't '
...
ffff800010cce56c t xhci_map_urb_for_dma
ffff800010cce56c t xhci_map_urb_for_dma.86d975cb70058c10e8ae4c2960627264
ffff800011227f28 t xhci_map_urb_for_dma.86d975cb70058c10e8ae4c2960627264.cfi_jt
...
so I think it's not just the `.cfi_jt` that we want to truncate. Sami
asked me about sending a v5 for
https://lore.kernel.org/lkml/20210707181814.365496-1-ndesaulniers@google.com/;
I was looking to rebase your v5 on my patch, but Sami also noted that
here https://lore.kernel.org/lkml/CABCJKue5Ay6_+8sibzh5wRh3gPzV1g72gJ9m2ot4E1ezj8bpHA@mail.gmail.com/
that the separator was changed from $ to . for other CFI symbols in
clang-13.
So I think I'm going to "combine" our patches to truncate after the
first `.` as long as CONFIG_LTO_CLANG is enabled, but still check for
`$` for clang-12 for CONFIG_CFI_CLANG. I will credit you with the
Suggested-by tag; stay tuned.
>
> Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
> ---
> Change in v5:
> - Also remove explcit config check for postfix ".llvm." as LLVM
> renames even in full LTO case
>
> Change in v4:
> - Remove redundant check; irrespective of LTO type (THIN/FULL),
> LTO_CLANG will be always enabled. Hence will be used as entry flag
> to check various postfix patterns.
> - And prior to stripping postfix ".cfi_jt", added a comment to
> justify why we are doing so.
>
> Change in v3:
> - Modified commit message to indicate fix is for Clang CFI postfix
> - Rebased on recent patch from ndesaulniers@google.com.
> https://lore.kernel.org/lkml/
> 20210707181814.365496-1-ndesaulniers@google.com/#t
> - Fix is enabled even for CONFIG_LTO_CLANG
>
> Change in v2:
> - Use existing routine in kallsyms to strip postfix ".cfi_jt" from
> extern function name.
> - Modified the commit message accordingly
>
> kernel/kallsyms.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 5cabe4dd3ff4..c8ef618e2a71 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -174,7 +174,7 @@ static bool cleanup_symbol_name(char *s)
> * foo.llvm.974640843467629774. This can break hooking of static
> * functions with kprobes.
> */
> - if (!IS_ENABLED(CONFIG_LTO_CLANG_THIN))
> + if (!IS_ENABLED(CONFIG_LTO_CLANG))
> return false;
>
> res = strstr(s, ".llvm.");
> @@ -194,6 +194,17 @@ static bool cleanup_symbol_name(char *s)
> return false;
>
> res = strrchr(s, '$');
> + if (!res) {
> + /*
> + * In case of non static function symbol <funcsym>,
> + * the local jump table will have entry as <funcsym>.cfi_jt.
> + *
> + * Such expansion breaks some built-in components,
> + * e.g. syscall tracer. Hence remove postfix ".cfi_jt".
> + */
> + res = strstr(s, ".cfi_jt");
> + }
> +
> if (res) {
> *res = '\0';
> return true;
> --
> 2.17.1
>
--
Thanks,
~Nick Desaulniers
prev parent reply other threads:[~2021-10-01 18:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210727131853.GA18032@pswork>
2021-07-27 14:06 ` [PATCH v2] kallsyms: strip ThinLTO postfix ".cfi_jt" Padmanabha Srinivasaiah
2021-07-28 20:57 ` Sami Tolvanen
2021-07-29 15:29 ` Padmanabha Srinivasaiah
2021-07-29 20:53 ` [PATCH v3] kallsyms: strip CLANG CFI " Padmanabha Srinivasaiah
2021-08-03 16:28 ` Sami Tolvanen
2021-08-04 17:17 ` Padmanabha Srinivasaiah
2021-08-05 23:27 ` [PATCH v4] " Padmanabha Srinivasaiah
2021-08-12 23:05 ` Sami Tolvanen
2021-08-14 12:15 ` Padmanabha Srinivasaiah
2021-08-14 12:42 ` [PATCH v5] " Padmanabha Srinivasaiah
2021-10-01 18:29 ` Nick Desaulniers [this message]
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