From 2932b4d05e1d212259c2903fd9cebcee5616680b Mon Sep 17 00:00:00 2001 From: Tony Ambardar Date: Fri, 14 Aug 2020 07:43:36 -0700 Subject: [PATCH] kernel: mips: fix init crash/bootloop on 64-bit systems The malta subtargets for mips64 and mips64el fail to start the init process at boot, resulting in a boot loop. The issue was raised and analyzed within FS#3277. Investigation suggested code near the [vdso] memory area of the process was long jumping into a region inaccessible to the process, e.g. init: - preinit - init: Launched preinit instance, pid=522 do_page_fault(): sending SIGSEGV to init for invalid read access from 0000000000000360 epc = 0000000000000360 in init[aaab42b000+4000] ra = 000000fffee385e0 in Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b Rebooting in 1 seconds.. Note the low-memory read access and epc are the same. Upstream kernel 5.6 included a relevant patch and discussion: * d3f703c4359f ("mips: vdso: fix 'jalr t9' crash in vdso code") Disassembly of the failing kernel's vdso.so confirmed presence of the telltale long jumps, e.g.: 00000000000007c0 <__vdso_clock_getres@@LINUX_2.6>: [...] 7dc: 0320f809 jalr t9 [...] Restore booting mips64/mips64el malta by backporting the above commit: * 310-v5.6-mips-vdso-fix-jalr-t9-crash-in-vdso-code.patch Fixes: 54310a3aa02f ("malta: add kernel 5.4 config") Fixes: FS#3277 Ref: https://bugs.openwrt.org/index.php?do=details&task_id=3277 Signed-off-by: Tony Ambardar --- ...-vdso-fix-jalr-t9-crash-in-vdso-code.patch | 59 +++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 target/linux/generic/backport-5.4/310-v5.6-mips-vdso-fix-jalr-t9-crash-in-vdso-code.patch diff --git a/target/linux/generic/backport-5.4/310-v5.6-mips-vdso-fix-jalr-t9-crash-in-vdso-code.patch b/target/linux/generic/backport-5.4/310-v5.6-mips-vdso-fix-jalr-t9-crash-in-vdso-code.patch new file mode 100644 index 0000000000..20551d81dc --- /dev/null +++ b/target/linux/generic/backport-5.4/310-v5.6-mips-vdso-fix-jalr-t9-crash-in-vdso-code.patch @@ -0,0 +1,59 @@ +From d3f703c4359ff06619b2322b91f69710453e6b6d Mon Sep 17 00:00:00 2001 +From: Victor Kamensky +Date: Tue, 11 Feb 2020 11:24:33 -0800 +Subject: [PATCH] mips: vdso: fix 'jalr t9' crash in vdso code + +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 +Signed-off-by: Victor Kamensky +Signed-off-by: Paul Burton +Cc: linux-mips@vger.kernel.org +Cc: Ralf Baechle +Cc: James Hogan +Cc: Vincenzo Frascino +Cc: richard.purdie@linuxfoundation.org +--- + arch/mips/vdso/Makefile | 1 + + 1 file changed, 1 insertion(+) + +diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile +index aa89a41dc5dd..848baeaef1f8 100644 +--- a/arch/mips/vdso/Makefile ++++ b/arch/mips/vdso/Makefile +@@ -33,6 +33,7 @@ endif + cflags-vdso := $(ccflags-vdso) \ + $(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \ + -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \ ++ -mrelax-pic-calls -mexplicit-relocs \ + -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \ + $(call cc-option, -fno-asynchronous-unwind-tables) \ + $(call cc-option, -fno-stack-protector) +-- +2.17.1 +