Messages in this thread | | | Date | Wed, 2 Jun 2021 12:32:40 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] arm64: vmlinux.lds.S: keep .entry.tramp.text section |
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On Tue, Mar 16, 2021 at 07:09:23PM +0000, Catalin Marinas wrote: > On Tue, Mar 16, 2021 at 05:39:27PM +0100, Arnd Bergmann wrote: > > On Tue, Mar 16, 2021 at 5:27 PM Catalin Marinas <catalin.marinas@arm.com> wrote: > > > On Tue, Mar 16, 2021 at 10:45:32AM +0000, Catalin Marinas wrote: > > > > On Fri, Feb 26, 2021 at 08:32:57PM -0800, Fangrui Song wrote: > > > > > On 2021-02-26, Kees Cook wrote: > > > > > > On Fri, Feb 26, 2021 at 03:03:39PM +0100, Arnd Bergmann wrote: > > > > > > > From: Arnd Bergmann <arnd@arndb.de> > > > > > > > > > > > > > > When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION, > > > > > > > I sometimes see an assertion > > > > > > > > > > > > > > ld.lld: error: Entry trampoline text too big > > > > > > > > > > > > Heh, "too big" seems a weird report for having it discarded. :) > > > > > > > > > > > > Any idea on this Fangrui? > > > > > > > > > > > > ( I see this is https://github.com/ClangBuiltLinux/linux/issues/1311 ) > > > > > > > > > > This diagnostic is from an ASSERT in arch/arm64/kernel/vmlinux.lds > > > > > > > > > > ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == (1 << 16), > > > > > "Entry trampoline text too big") > > > > > > > > Can we not change the ASSERT to be <= PAGE_SIZE instead? > > > > > > Ah, that won't work as I suspect we still need the trampoline section. > > > > > > Arnd, do you know why this section disappears? I did a simple test with > > > defconfig + LD_DEAD_CODE_DATA_ELIMINATION and the trampoline section is > > > still around. > > > > If I remember correctly, this showed up when CONFIG_ARM_SDE_INTERFACE > > is disabled, which dropped the only reference into this section. > > If that doesn't make sense, I can try digging through the old build logs to > > reproduce the problem. > > I suspected this as well but still worked for me when disabling it. > > Anyway, I don't think identifying the exact option is necessary. With > CONFIG_UNMAP_KERNEL_AT_EL0=y we need this section around even if only > __entry_tramp_text_start/end are referenced. > > In this case we happened to detect this issue because of the ASSERT in > vmlinux.lds.S but I wonder what else the linker drops with this dead > code elimination that we may not notice (it seems to remove about 500KB > from the resulting image in my test). > > I'll push these two patches to -next for wider coverage before deciding > on mainline (though the option may not get much testing as it's hidden > behind EXPERT and default n).
I don't see this in -next? Catalin, do you want me to pick it up as part of my collecting various linker fixes?
-Kees
-- Kees Cook
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