2019-06-28 17:24:39

by Vasily Gorbik

Subject: [PATCH] kallsyms: exclude kasan local symbols on s390

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 <[email protected]>
---
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

2019-07-06 14:17:41

by Masahiro Yamada

Subject: Re: [PATCH] kallsyms: exclude kasan local symbols on s390

On Sat, Jun 29, 2019 at 2:22 AM Vasily Gorbik <[email protected]> wrote:
>
> 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 <[email protected]>

Applied to linux-kbuild. Thanks.




> ---
> 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
>


--
Best Regards
Masahiro Yamada