| 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: <20220413132359.GA8987@pswork>
Date: Wed, 13 Apr 2022 15:23:59 +0200
From: Padmanabha Srinivasaiah <treasure4paddy@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
Randy Dunlap <rdunlap@...radead.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev,
Masahiro Yamada <masahiroy@...nel.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v4 0/3] bootconfig: Support embedding a bootconfig in
kernel for non initrd boot
Hello Masami Hiramatsu,
Sorry for long delay, was out of town.
>On Sun, Mar 27, 2022 at 11:55:26AM +0900, Masami Hiramatsu wrote:
> Hi Padmanabha,
>
> On Sun, 27 Mar 2022 08:53:06 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> >
> > KNOWN ISSUE:
> >
> > According to the report from Padmanabha[3], the embedded bootconfig data may not
> > be updated if you do incremental build the kernel with CONFIG_LTO. This is
> > under investigation.
>
> I tried to test this version with LTO_CLANG_FULL and LTO_CLANG_THIN with
> switching the embedded bootconfig file by CONFIG_EMBED_BOOT_CONFIG_FILE (on x86).
>
> I found that when I use LTO_CLANG_FULL, the embedded bootconfig was updated
> correctly.
> But with the LTO_CLANG_THIN, the embedded bootconfig was *NOT* updated.
>
> I used the latest prebuild llvm 15.0.0 on x86 [4]. Padmanabha, can you confirm
> with this latest LLVM? I guess something wrong with your old LLVM.
>
> [4] https://download.01.org/0day-ci/cross-package/clang-latest/clang-latest/clang.tar.xz
>
Thanks for the link for prebuilt llvm 15.0.0.
[p1] https://www.spinics.net/lists/kernel/msg4307362.html
With llvm 15.0.0 and latest patchset v8 for bootconfig [p1] on arm64 the
test observations are:
For bootconfig:
I dont observe anymore an issue with incremental builds, irresepctive of LTO
type selected: FULL/THIN.
For config.gz:
The test observations is exactly similar to yours.
With LTO_CLANG_THIN configs were *NOT* updated.
But with LTO_CLANG_FULL confs were updated.
Test results validates and confirms your earlier analysis on issue with
inline asm and .incbin directive and THIN_LTO.
> Here is the test procedure.
>
> 1. Prepare 2 different bootconfig files (bconf1, bconf2).
> 2. Configure kernel with LTO_CLANG and setting the full path of bconf1 to
> CONFIG_EMBED_BOOT_CONFIG_FILE.
> 3. Build the kernel
> 4. Boot the kernel with "bootconfig" in the kernel cmdline.
> 5. Check the /proc/bootconfig is same as bconf1.
> 6. Reconfigure kernel with the full path of *bconf2* to CONFIG_EMBED_BOOT_CONFIG_FILE.
> 7. Rebuild the kernel (no cleanup)
> 8. Boot the kernel with "bootconfig" in the kernel cmdline.
> 9. Check the /proc/bootconfig is same as bconf2.
>
> So with LTO_CLANG_FULL, at the step 9 /proc/bootconfig shows bconf2, but with
> LTO_CLANG_THIN, it shows bconf1.
>
> In both cases, build log showed that the default.bconf was updated (I confirmed the
> lib/default.bconf is updated)
>
> UPD lib/default.bconf
> CC lib/bootconfig.o
> AR lib/lib.a
>
>
> Here is my guess. I found that when we enable LTO_CLANG, the compiler compiles
> C source file into LLVM IR bitcode.
>
> $ file work/linux/build-x86_64/lib/bootconfig.o
> work/linux/build-x86_64/lib/bootconfig.o: LLVM IR bitcode
>
> This means at this point the object file doesn't include the lib/default.bconf
> because it will be embedded by assembler. The bitcode seems only have the
> inline asm code (which only has an .incbin directive) as a constatns block[5].
>
> [5]
> Block ID #11 (CONSTANTS_BLOCK):
> Num Instances: 32
> Total Size: 54305b/6788.12B/1697W
> Percent of file: 19.9792%
> Average Size: 1697.03/212.13B/53W
> Tot/Avg SubBlocks: 0/0.000000e+00
> Tot/Avg Abbrevs: 4/1.250000e-01
> Tot/Avg Records: 486/1.518750e+01
> Percent Abbrevs: 80.8642%
>
> Record Histogram:
> Count # Bits b/Rec % Abv Record Kind
> 219 4860 22.2 100.00 INTEGER
> 144 1728 12.0 100.00 SETTYPE
> 41 656 16.0 NULL
> 39 2970 76.2 CE_INBOUNDS_GEP
> 26 3504 134.8 100.00 CSTRING
> 10 37720 3772.0 INLINEASM
> 4 96 24.0 100.00 CE_CAST
> 1 58 CE_CMP
> 1 52 CE_SELECT
> 1 46 CE_BINOP
>
> And when the LLVM runs LTO with THIN mode, it might not update (not rebuild to
> machine code) that inline asm code block because that block is not updated.
> I confirmed that the block (bootconfig.o) is not updated after rebuilding
> the kernel as below.
>
Yes, thanks for details. Analysis is in sync with observations from test
results.
Thanks and Regards,
Padmanabha.S
> After step 3.
> $ llvm-bcanalyzer work/linux/build-x86_64/lib/bootconfig.o > bconf.dump1
> After step 7.
> $ llvm-bcanalyzer work/linux/build-x86_64/lib/bootconfig.o > bconf.dump2
> $ diff bconf.dump*
> (No difference)
>
> Thank you,
>
> >
> > [3] https://lore.kernel.org/all/20220321183500.GA4065@pswork/T/#u
> >
> > Thank you,
> >
> > ---
> >
> > Masami Hiramatsu (3):
> > bootconfig: Check the checksum before removing the bootconfig from initrd
> > bootconfig: Support embedding a bootconfig file in kernel
> > docs: bootconfig: Add how to embed the bootconfig into kernel
> >
> >
> > Documentation/admin-guide/bootconfig.rst | 30 ++++++++++++++++++++++++++---
> > include/linux/bootconfig.h | 10 ++++++++++
> > init/Kconfig | 21 ++++++++++++++++++++
> > init/main.c | 31 +++++++++++++++---------------
> > lib/.gitignore | 1 +
> > lib/Makefile | 10 ++++++++++
> > lib/bootconfig.c | 23 ++++++++++++++++++++++
> > 7 files changed, 108 insertions(+), 18 deletions(-)
> >
> > --
> > Masami Hiramatsu (Linaro) <mhiramat@...nel.org>
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>
Powered by blists - more mailing lists