Messages in this thread | | | Date | Sat, 29 Aug 2020 22:23:30 -0400 | From | Sasha Levin <> | Subject | Re: [PATCH AUTOSEL 5.4 10/58] mips: vdso: fix 'jalr t9' crash in vdso code |
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On Sat, Aug 29, 2020 at 04:37:32PM +0200, Hauke Mehrtens wrote: >On 8/29/20 3:56 PM, Sasha Levin wrote: >> On Sat, Aug 29, 2020 at 03:08:01PM +0200, Hauke Mehrtens wrote: >>> On 3/5/20 6:13 PM, Sasha Levin wrote: >>>> From: Victor Kamensky <kamensky@cisco.com> >>>> >>>> [ Upstream commit d3f703c4359ff06619b2322b91f69710453e6b6d ] >>>> >>>> Observed that when kernel is built with Yocto mips64-poky-linux-gcc, >>>> and mips64-poky-linux-gnun32-gcc toolchain, resulting vdso contains >>>> 'jalr t9' instructions in its code and since in vdso case nobody >>>> sets GOT table code crashes when instruction reached. On other hand >>>> observed that when kernel is built mips-poky-linux-gcc toolchain, the >>>> same 'jalr t9' instruction are replaced with PC relative function >>>> calls using 'bal' instructions. >>>> >>>> The difference boils down to -mrelax-pic-calls and -mexplicit-relocs >>>> gcc options that gets different default values depending on gcc >>>> target triplets and corresponding binutils. -mrelax-pic-calls got >>>> enabled by default only in mips-poky-linux-gcc case. MIPS binutils >>>> ld relies on R_MIPS_JALR relocation to convert 'jalr t9' into 'bal' >>>> and such relocation is generated only if -mrelax-pic-calls option >>>> is on. >>>> >>>> Please note 'jalr t9' conversion to 'bal' can happen only to static >>>> functions. These static PIC calls use mips local GOT entries that >>>> are supposed to be filled with start of DSO value by run-time linker >>>> (missing in VDSO case) and they do not have dynamic relocations. >>>> Global mips GOT entries must have dynamic relocations and they should >>>> be prevented by cmd_vdso_check Makefile rule. >>>> >>>> Solution call out -mrelax-pic-calls and -mexplicit-relocs options >>>> explicitly while compiling MIPS vdso code. That would get correct >>>> and consistent between different toolchains behaviour. >>>> >>>> Reported-by: Bruce Ashfield <bruce.ashfield@gmail.com> >>>> Signed-off-by: Victor Kamensky <kamensky@cisco.com> >>>> Signed-off-by: Paul Burton <paulburton@kernel.org> >>>> Cc: linux-mips@vger.kernel.org >>>> Cc: Ralf Baechle <ralf@linux-mips.org> >>>> Cc: James Hogan <jhogan@kernel.org> >>>> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> >>>> Cc: richard.purdie@linuxfoundation.org >>>> Signed-off-by: Sasha Levin <sashal@kernel.org> >>>> --- >>>> arch/mips/vdso/Makefile | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>> >>> Hi Sasha, >>> >>> Why was this not added to the 5.4 stable branch? >>> >>> Some OpenWrt users ran into this problem with kernel 5.4 on MIPS64 [0]. >>> We backported this patch on our own in OpenWrt [1], but it should be >>> added to the sable branch in my opinion as it fixes a real problem. >>> >>> @Sasha: Can you add it to the 5.4 stable branch or should I send some >>> special email? >> >> It failed building on 5.4. If you'd like it included, please send me a >> tested backport for 5.4. >> > >I successfully compiled a kernel 5.4.61 with this patch on top with GCC >8.4 for MIPS 64 big and little Endian. > >What was broken in your compile test?
See https://lore.kernel.org/stable/bfdce3ef-5fe9-8dab-1695-be3d33727529@roeck-us.net/
-- Thanks, Sasha
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