On Tue, Feb 13, 2018 at 4:37 PM, Kees Cook <keesc...@chromium.org> wrote: > On Tue, Feb 13, 2018 at 8:57 AM, tedheadster <tedheads...@gmail.com> wrote: >> Changing X86_32_LAZY_GS to 'y' does not cause the kernel to hang. >> >>> On Tue, Feb 13, 2018 at 11:40:17AM -0500, tedheadster wrote: >>>> in your patch "x86: make lazy %gs optional on x86_32" were you able >>>> to test it on really old processors? In 4.16.0-rc1, X86_32_LAZY_GS got >>>> toggled from 'y' to 'n' in my default config because of changes to the >>>> stack protector code. It hangs my ancient i486 test machine right >>>> after 'Booting the kernel'. >>> >>> I didn't have access to an i486 at the time or ever since, so it >>> wasn't tested there. If this is specific to i486, flagging it so in >>> the config probably isn't the end of the world at this point. >> >> Tejun, >> I will be able to test this on other 32bit hardware at the end of >> the week. Hopefully I'll be able to identify which processors it does >> not work on (i486/i586/i686). > > So, this is the exact opposite of my tests: if I had X86_32_LAZY_GS=y > and stack protector enabled (via _AUTO), the boot would hang. This > change solved that for me: > > config X86_32_LAZY_GS > def_bool y > - depends on X86_32 && !CC_STACKPROTECTOR > + depends on X86_32 && CC_STACKPROTECTOR_NONE > > since stack-protector in _AUTO mode had to reorganize that logic. It > seemed LAZY_GS isn't compatible with stack-protector, so I made sure > to retain that. What are your other configs? >
Kees, I am running the 4.16-rc1 release. My arch/x86/Kconfig has this logic: config X86_32_LAZY_GS def_bool y depends on X86_32 && CC_STACKPROTECTOR_NONE I get a hang on i486 when I choose any of these configuration options: CONFIG_CC_STACKPROTECTOR_AUTO=y CONFIG_CC_STACKPROTECTOR_REGULAR=y CONFIG_CC_STACKPROTECTOR_STRONG=y Also, CONFIG_X86_32_LAZY_GS does not appear in any of these config files, not even as "# CONFIG_X86_32_LAZY_GS is not set", which I thought was strange. The only configuration that works on i486 is: CONFIG_CC_STACKPROTECTOR_NONE=y CONFIG_X86_32_LAZY_GS=y Now it gets interesting. All four of these configurations boots successfully when compiled for, and run on, a Pentium 4 M (CONFIG_PENTIUM4). So it certainly is related to what version of the processor you use. I will continue to try other configuration combinations and report back. - Matthew