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: <1403477209-14612-1-git-send-email-minipli@googlemail.com> Date: Mon, 23 Jun 2014 00:46:46 +0200 From: Mathias Krause <minipli@...glemail.com> To: linux-kernel@...r.kernel.org Cc: Andrew Morton <akpm@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Steven Rostedt <rostedt@...dmis.org>, Joe Perches <joe@...ches.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>, Mathias Krause <minipli@...glemail.com> Subject: [RFC PATCH 0/3] Mark literal strings in __init / __exit code This RFC series tries to address the problem of dangling strings of __init functions after initialization, as well as __exit strings for code not even included in the final kernel image. The code might get freed, but the format strings are not. One solution to the problem might be to declare variables in the code and mark those variables as __initconst. That, though, makes the code ugly, as can be seen, e.g., in drivers/hwmon/w83627ehf.c -- a pile of 'static const char[] __initconst' lines just for the pr_info() call. To be able to mark strings easily patch 1 adds macros to init.h to do so without the need to explicitly define variables in the code. Internally it'll declare ones nonetheless, as this seem to be the only way to attach an __attribute__() to a verbatim string. That's already enough to solve the problem -- mark the corresponding stings by using these macros. But patch 2 adds some syntactical sugar for the most popular use case, by providing pr_<level> alike macros, namely pi_<level> for __init code and pe_<level> for __exit code. This hides the use of the marker macros behind the commonly known printing functions -- with just a single character changed. Patch 3 exemplarily changes all strings and format strings in arch/x86/kernel/acpi/boot.c to use the new macros. It also addresses a few styling issues, though. But this already leads to ~1.7 kB of r/o data moved to the .init.rodata section, marking it for release after init. Open issues with this approach: 1/ When CONFIG_DYNAMIC_DEBUG is enabled, pi_debug() and pe_debug() fall-back to pr_debug() as there is currently no way of removing the dynamic entries from the dynamic debug code after init. 2/ The variables used in the macros of patch 1 will pollute the symtab with unneeded entries. That'll be a problem in the KALLSYMS_ALL case only, though. But the symtab will be huge then, anyway. However, filtering those even in this case might be desirable. 3/ It only seamlessly integrates for the pr_<level>() kind of use cases. For other literal strings it gets slightly less readable, e.g. this: strncmp(str, "s4_nohwsig", 10) becomes this: strncmp(str, __init_str("s4_nohwsig"), 10) That might be okay, though, as it marks the string clearly as an init string, so might actually increase the understanding of the life time of the string literal. So, is there interest in having such macros and markings? Patch 3 shows, that there's actual value in it. A hacked up script, dully changing pr_<level> to pi_<level> for __init functions under arch/x86/ already is able to move ~8kB of r/o data into the .init section. The script, though, is dump. It does not handle any of the printk() calls, nor does it handle panic() calls or other strings used only in initialization code. So there's more to squeeze out. I just want to get some feedback first. Also documentation of the new macros is missing, maybe even a checkpatch.pl change to propose using the new macros instead of pr_*() or plain printk() in __init / __exit functions. What do you think? Regards, Mathias Mathias Krause (3): init.h: Add __init_str / __exit_str macros printk: Provide pi_<level> / pe_<level> macros for __init / __exit code x86, acpi: Mark __init strings as such arch/x86/kernel/acpi/boot.c | 162 ++++++++++++++++++++----------------------- include/linux/init.h | 18 +++++ include/linux/printk.h | 52 ++++++++++++++ 3 files changed, 144 insertions(+), 88 deletions(-) -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists