Messages in this thread | | | Date | Sat, 29 Aug 2020 09:56:56 -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 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.
-- Thanks, Sasha
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