| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <046baaea-217f-4ecc-b340-b5f6f1cee0b9@intel.com>
Date: Mon, 5 Feb 2024 08:58:05 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
Ian Rogers <irogers@...gle.com>, Like Xu <like.xu.linux@...il.com>,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/2] perf symbols: Slightly improve module file executable
section mappings
On 3/02/24 03:44, Namhyung Kim wrote:
> Hi Adrian,
>
> On Fri, Feb 02, 2024 at 01:01:30PM +0200, Adrian Hunter wrote:
>> Currently perf does not record module section addresses except for
>> the .text section. In general that means perf cannot get module section
>> mappings correct (except for .text) when loading symbols from a kernel
>> module file. (Note using --kcore does not have this issue)
>>
>> Improve that situation slightly by identifying executable sections that
>> use the same mapping as the .text section. That happens when an
>> executable section comes directly after the .text section, both in memory
>> and on file, something that can be determined by following the same layout
>> rules used by the kernel, refer kernel layout_sections(). Note whether
>> that happens is somewhat arbitrary, so this is not a final solution.
>>
>> Example from tracing a virtual machine process:
>>
>> Before:
>>
>> $ perf script | grep unknown
>> CPU 0/KVM 1718 203.511270: 318341 cpu-cycles:P: ffffffffc13e8a70 [unknown] (/lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko)
>> $ perf script -vvv 2>&1 >/dev/null | grep kvm.intel | grep 'noinstr.text\|ffff'
>> Map: 0-7e0 41430 [kvm_intel].noinstr.text
>> Map: ffffffffc13a7000-ffffffffc1421000 a0 /lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko
>>
>> After:
>>
>> $ perf script | grep 203.511270
>> CPU 0/KVM 1718 203.511270: 318341 cpu-cycles:P: ffffffffc13e8a70 vmx_vmexit+0x0 (/lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko)
>> $ perf script -vvv 2>&1 >/dev/null | grep kvm.intel | grep 'noinstr.text\|ffff'
>> Map: ffffffffc13a7000-ffffffffc1421000 a0 /lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko
>>
>> Reported-by: Like Xu <like.xu.linux@...il.com>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>> tools/perf/util/symbol-elf.c | 75 +++++++++++++++++++++++++++++++++++-
>> 1 file changed, 73 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index 9e7eeaf616b8..98bf0881aaf6 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -23,6 +23,7 @@
>> #include <linux/ctype.h>
>> #include <linux/kernel.h>
>> #include <linux/zalloc.h>
>> +#include <linux/string.h>
>> #include <symbol/kallsyms.h>
>> #include <internal/lib.h>
>>
>> @@ -1329,6 +1330,58 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>> return -1;
>> }
>>
>> +static bool is_exe_text(int flags)
>> +{
>> + return (flags & (SHF_ALLOC | SHF_EXECINSTR)) == (SHF_ALLOC | SHF_EXECINSTR);
>> +}
>> +
>> +/*
>> + * Some executable module sections like .noinstr.text might be laid out with
>> + * .text so they can use the same mapping (memory address to file offset).
>> + * Check if that is the case. Refer to kernel layout_sections(). Return the
>> + * maximum offset.
>> + */
>> +static u64 max_text_section(Elf *elf, GElf_Ehdr *ehdr)
>> +{
>> + Elf_Scn *sec = NULL;
>> + GElf_Shdr shdr;
>> + u64 offs = 0;
>> +
>> + /* Doesn't work for some arch */
>> + if (ehdr->e_machine == EM_PARISC ||
>> + ehdr->e_machine == EM_ALPHA)
>> + return 0;
>> +
>> + /* ELF is corrupted/truncated, avoid calling elf_strptr. */
>> + if (!elf_rawdata(elf_getscn(elf, ehdr->e_shstrndx), NULL))
>> + return 0;
>> +
>> + while ((sec = elf_nextscn(elf, sec)) != NULL) {
>> + char *sec_name;
>> +
>> + if (!gelf_getshdr(sec, &shdr))
>> + break;
>> +
>> + if (!is_exe_text(shdr.sh_flags))
>> + continue;
>> +
>> + /* .init and .exit sections are not placed with .text */
>> + sec_name = elf_strptr(elf, ehdr->e_shstrndx, shdr.sh_name);
>> + if (!sec_name ||
>> + strstarts(sec_name, ".init") ||
>> + strstarts(sec_name, ".exit"))
>> + break;
>
> Do we really need this? It seems my module has .init.text section
> next to .text.
>
> $ readelf -SW /lib/modules/`uname -r`/kernel/fs/ext4/ext4.ko
> There are 77 section headers, starting at offset 0x252e90:
>
> Section Headers:
> [Nr] Name Type Address Off Size ES Flg Lk Inf Al
> [ 0] NULL 0000000000000000 000000 000000 00 0 0 0
> [ 1] .text PROGBITS 0000000000000000 000040 079fa7 00 AX 0 0 16
> [ 2] .rela.text RELA 0000000000000000 13c348 04f0c8 18 I 74 1 8
> [ 3] .init.text PROGBITS 0000000000000000 079ff0 00060c 00 AX 0 0 16
> ...
>
>
> ALIGN(0x40 + 0x79fa7, 16) = 0x79ff0, right?
But not in memory e.g.
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 3] .text PROGBITS 0000000000000000 0000a0 071719 00 AX 0 0 16
[ 5] .text.unlikely PROGBITS 0000000000000000 0717b9 000a59 00 AX 0 0 1
[ 7] .init.text PROGBITS 0000000000000000 072212 0004fe 00 AX 0 0 1
[ 9] .altinstr_replacement PROGBITS 0000000000000000 072710 000004 00 AX 0 0 1
[10] .static_call.text PROGBITS 0000000000000000 072714 000388 00 AX 0 0 4
[12] .exit.text PROGBITS 0000000000000000 072a9c 000078 00 AX 0 0 1
/sys/module/ext4/sections/.text: 0xffffffffc0453000
/sys/module/ext4/sections/.text.unlikely: 0xffffffffc04c4719
/sys/module/ext4/sections/.init.text: 0xffffffffc053e000
/sys/module/ext4/sections/.altinstr_replacement: 0xffffffffc04c5172
/sys/module/ext4/sections/.static_call.text: 0xffffffffc04c5178
/sys/module/ext4/sections/.exit.text: 0xffffffffc04c5500
Need to have:
section address - offset == .text address - .text offset
perf does not record the section address, but the kernel
layout_sections() lays out executable sections in order
starting with .text *until* it gets to .init* or .exit*.
Powered by blists - more mailing lists