Re: [PATCH 5.10 103/157] MIPS: kernel: Reserve exception base early to prevent corruption

[Greg Kroah-Hartman]

On Mon, Mar 22, 2021 at 07:44:05PM +0530, Naresh Kamboju wrote:
> On Mon, 22 Mar 2021 at 18:14, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > From: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> >
> > [ Upstream commit bd67b711bfaa02cf19e88aa2d9edae5c1c1d2739 ]
> >
> > BMIPS is one of the few platforms that do change the exception base.
> > After commit 2dcb39645441 ("memblock: do not start bottom-up allocations
> > with kernel_end") we started seeing BMIPS boards fail to boot with the
> > built-in FDT being corrupted.
> >
> > Before the cited commit, early allocations would be in the [kernel_end,
> > RAM_END] range, but after commit they would be within [RAM_START +
> > PAGE_SIZE, RAM_END].
> >
> > The custom exception base handler that is installed by
> > bmips_ebase_setup() done for BMIPS5000 CPUs ends-up trampling on the
> > memory region allocated by unflatten_and_copy_device_tree() thus
> > corrupting the FDT used by the kernel.
> >
> > To fix this, we need to perform an early reservation of the custom
> > exception space. Additional we reserve the first 4k (1k for R3k) for
> > either normal exception vector space (legacy CPUs) or special vectors
> > like cache exceptions.
> >
> > Huge thanks to Serge for analysing and proposing a solution to this
> > issue.
> >
> > Fixes: 2dcb39645441 ("memblock: do not start bottom-up allocations with kernel_end")
> > Reported-by: Kamal Dasu <kdasu.kdev@xxxxxxxxx>
> > Debugged-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
> > Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > Tested-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > Reviewed-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> > Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  arch/mips/include/asm/traps.h    |  3 +++
> >  arch/mips/kernel/cpu-probe.c     |  6 ++++++
> >  arch/mips/kernel/cpu-r3k-probe.c |  3 +++
> >  arch/mips/kernel/traps.c         | 10 +++++-----
> 
> mipc tinyconfig and allnoconfig builds failed on stable-rc 5.10 branch
> 
> make --silent --keep-going --jobs=8
> O=/home/tuxbuild/.cache/tuxmake/builds/1/tmp ARCH=mips
> CROSS_COMPILE=mips-linux-gnu- 'CC=sccache mips-linux-gnu-gcc'
> 'HOSTCC=sccache gcc'
> WARNING: modpost: vmlinux.o(.text+0x6a88): Section mismatch in
> reference from the function reserve_exception_space() to the function
> .meminit.text:memblock_reserve()
> The function reserve_exception_space() references
> the function __meminit memblock_reserve().
> This is often because reserve_exception_space lacks a __meminit
> annotation or the annotation of memblock_reserve is wrong.
> 
> FATAL: modpost: Section mismatches detected.
> Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
> make[2]: *** [/builds/linux/scripts/Makefile.modpost:59:
> vmlinux.symvers] Error 1
> 
> Here is the list of build failed,
>  - gcc-8-allnoconfig
>  - gcc-8-tinyconfig
>  - gcc-9-allnoconfig
>  - gcc-9-tinyconfig
>  - gcc-10-allnoconfig
>  - gcc-10-tinyconfig
>  - clang-10-tinyconfig
>  - clang-10-allnoconfig
>  - clang-11-allnoconfig
>  - clang-11-tinyconfig
>  - clang-12-tinyconfig
>  - clang-12-allnoconfig
> 
> Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> 
> link:
> https://gitlab.com/Linaro/lkft/mirrors/stable/linux-stable-rc/-/jobs/1117167411#L142
> 
> steps to reproduce:
> ---------------------------
> # TuxMake is a command line tool and Python library that provides
> # portable and repeatable Linux kernel builds across a variety of
> # architectures, toolchains, kernel configurations, and make targets.
> #
> # TuxMake supports the concept of runtimes.
> # See https://docs.tuxmake.org/runtimes/, for that to work it requires
> # that you install podman or docker on your system.
> #
> # To install tuxmake on your system globally:
> # sudo pip3 install -U tuxmake
> #
> # See https://docs.tuxmake.org/ for complete documentation.
> 
> 
> tuxmake --runtime podman --target-arch mips --toolchain gcc-10
> --kconfig tinyconfig
> 

Thanks for letting me know, I'll go drop this and push out a new -rc...

greg k-h