linux-kernel - [PATCH v10 01/15] modpost: fix removing numeric suffixes

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Message-Id: <20220209185752.1226407-2-alexandr.lobakin@intel.com>
Date:   Wed,  9 Feb 2022 19:57:38 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     linux-hardening@...r.kernel.org, x86@...nel.org
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
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        Herbert Xu <herbert@...dor.apana.org.au>,
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        Masami Hiramatsu <mhiramat@...nel.org>,
        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: [PATCH v10 01/15] modpost: fix removing numeric suffixes

`-z unique-symbol` linker flag which is planned to use with FG-KASLR
to simplify livepatching (hopefully globally later on) triggers the
following:

ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL

The reason is that for now the condition from remove_dot():

if (m && (s[n + m] == '.' || s[n + m] == 0))

which was designed to test if it's a dot or a '\0' after the suffix
is never satisfied.
This is due to that `s[n + m]` always points to the last digit of a
numeric suffix, not on the symbol next to it (from a custom debug
print added to modpost):

param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'

So it's off-by-one and was like that since 2014.
Fix this for the sake of upcoming features, but don't bother
stable-backporting, as it's well hidden -- apart from that LD flag,
can be triggered only by GCC LTO which never landed upstream.

Fixes: fcd38ed0ff26 ("scripts: modpost: fix compilation warning")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
---
 scripts/mod/modpost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6bfa33217914..4648b7afe5cc 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1986,7 +1986,7 @@ static char *remove_dot(char *s)
 
 	if (n && s[n]) {
 		size_t m = strspn(s + n + 1, "0123456789");
-		if (m && (s[n + m] == '.' || s[n + m] == 0))
+		if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
 			s[n] = 0;
 
 		/* strip trailing .lto */
-- 
2.34.1