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Date:   Fri, 28 Jun 2019 19:22:47 +0200
From:   Vasily Gorbik <gor@linux.ibm.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>
Cc:     linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: [PATCH] kallsyms: exclude kasan local symbols on s390
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Message-Id: <patch.git-3ffb613bd7b2.your-ad-here.call-01561742434-ext-8011@work.hours>
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gcc asan instrumentation emits the following sequence to store frame pc
when the kernel is built with CONFIG_RELOCATABLE:
debug/vsprintf.s:
        .section        .data.rel.ro.local,"aw"
        .align  8
.LC3:
        .quad   .LASANPC4826@GOTOFF
.text
        .align  8
        .type   number, @function
number:
.LASANPC4826:

and in case reloc is issued for LASANPC label it also gets into .symtab
with the same address as actual function symbol:
$ nm -n vmlinux | grep 0000000001397150
0000000001397150 t .LASANPC4826
0000000001397150 t number

In the end kernel backtraces are almost unreadable:
[  143.748476] Call Trace:
[  143.748484] ([<000000002da3e62c>] .LASANPC2671+0x114/0x190)
[  143.748492]  [<000000002eca1a58>] .LASANPC2612+0x110/0x160
[  143.748502]  [<000000002de9d830>] print_address_description+0x80/0x3b0
[  143.748511]  [<000000002de9dd64>] __kasan_report+0x15c/0x1c8
[  143.748521]  [<000000002ecb56d4>] strrchr+0x34/0x60
[  143.748534]  [<000003ff800a9a40>] kasan_strings+0xb0/0x148 [test_kasan]
[  143.748547]  [<000003ff800a9bba>] kmalloc_tests_init+0xe2/0x528 [test_kasan]
[  143.748555]  [<000000002da2117c>] .LASANPC4069+0x354/0x748
[  143.748563]  [<000000002dbfbb16>] do_init_module+0x136/0x3b0
[  143.748571]  [<000000002dbff3f4>] .LASANPC3191+0x2164/0x25d0
[  143.748580]  [<000000002dbffc4c>] .LASANPC3196+0x184/0x1b8
[  143.748587]  [<000000002ecdf2ec>] system_call+0xd8/0x2d8

Since LASANPC labels are not even unique and get into .symtab only due
to relocs filter them out in kallsyms.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---
 scripts/kallsyms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index e17837f1d3f2..ae6504d07fd6 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -150,6 +150,9 @@ static int read_symbol(FILE *in, struct sym_entry *s)
 	/* exclude debugging symbols */
 	else if (stype == 'N' || stype == 'n')
 		return -1;
+	/* exclude s390 kasan local symbols */
+	else if (!strncmp(sym, ".LASANPC", 8))
+		return -1;
 
 	/* include the type field in the symbol name, so that it gets
 	 * compressed together */
-- 
2.21.0