2020-08-14 14:43:36 +00:00
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From d3f703c4359ff06619b2322b91f69710453e6b6d Mon Sep 17 00:00:00 2001
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From: Victor Kamensky <kamensky@cisco.com>
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Date: Tue, 11 Feb 2020 11:24:33 -0800
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Subject: [PATCH] mips: vdso: fix 'jalr t9' crash in vdso code
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Observed that when kernel is built with Yocto mips64-poky-linux-gcc,
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and mips64-poky-linux-gnun32-gcc toolchain, resulting vdso contains
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'jalr t9' instructions in its code and since in vdso case nobody
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sets GOT table code crashes when instruction reached. On other hand
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observed that when kernel is built mips-poky-linux-gcc toolchain, the
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same 'jalr t9' instruction are replaced with PC relative function
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calls using 'bal' instructions.
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The difference boils down to -mrelax-pic-calls and -mexplicit-relocs
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gcc options that gets different default values depending on gcc
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target triplets and corresponding binutils. -mrelax-pic-calls got
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enabled by default only in mips-poky-linux-gcc case. MIPS binutils
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ld relies on R_MIPS_JALR relocation to convert 'jalr t9' into 'bal'
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and such relocation is generated only if -mrelax-pic-calls option
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is on.
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Please note 'jalr t9' conversion to 'bal' can happen only to static
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functions. These static PIC calls use mips local GOT entries that
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are supposed to be filled with start of DSO value by run-time linker
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(missing in VDSO case) and they do not have dynamic relocations.
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Global mips GOT entries must have dynamic relocations and they should
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be prevented by cmd_vdso_check Makefile rule.
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Solution call out -mrelax-pic-calls and -mexplicit-relocs options
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explicitly while compiling MIPS vdso code. That would get correct
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and consistent between different toolchains behaviour.
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Reported-by: Bruce Ashfield <bruce.ashfield@gmail.com>
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Signed-off-by: Victor Kamensky <kamensky@cisco.com>
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Signed-off-by: Paul Burton <paulburton@kernel.org>
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Cc: linux-mips@vger.kernel.org
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Cc: Ralf Baechle <ralf@linux-mips.org>
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Cc: James Hogan <jhogan@kernel.org>
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Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
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Cc: richard.purdie@linuxfoundation.org
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---
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arch/mips/vdso/Makefile | 1 +
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1 file changed, 1 insertion(+)
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--- a/arch/mips/vdso/Makefile
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+++ b/arch/mips/vdso/Makefile
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2020-08-11 16:13:19 +00:00
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@@ -29,6 +29,7 @@ endif
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2020-08-14 14:43:36 +00:00
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cflags-vdso := $(ccflags-vdso) \
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$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
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-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
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+ -mrelax-pic-calls -mexplicit-relocs \
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-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
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$(call cc-option, -fno-asynchronous-unwind-tables) \
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$(call cc-option, -fno-stack-protector)
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