# git rev-parse -q --verify 006b445f18fa152c8e375abf4c68eab6d0b4afae^{commit} 006b445f18fa152c8e375abf4c68eab6d0b4afae already have revision, skipping fetch # git checkout -q -f -B kisskb 006b445f18fa152c8e375abf4c68eab6d0b4afae # git clean -qxdf # < git log -1 # commit 006b445f18fa152c8e375abf4c68eab6d0b4afae # Author: Alexey Kardashevskiy # Date: Tue Feb 2 20:15:41 2021 +1100 # # powerpc/kuap: Restore AMR after replaying soft interrupts # # Since de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace # Access Protection"), user access helpers call user_{read|write}_access_{begin|end} # when user space access is allowed. # # Commit 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") made # the mentioned helpers program a AMR special register to allow such # access for a short period of time, most of the time AMR is expected to # block user memory access by the kernel. # # Since the code accesses the user space memory, unsafe_get_user() calls # might_fault() which calls arch_local_irq_restore() if either # CONFIG_PROVE_LOCKING or CONFIG_DEBUG_ATOMIC_SLEEP is enabled. # arch_local_irq_restore() then attempts to replay pending soft # interrupts as KUAP regions have hardware interrupts enabled. # # If a pending interrupt happens to do user access (performance # interrupts do that), it enables access for a short period of time so # after returning from the replay, the user access state remains blocked # and if a user page fault happens - "Bug: Read fault blocked by AMR!" # appears and SIGSEGV is sent. # # An example trace: # Bug: Read fault blocked by AMR! # WARNING: CPU: 0 PID: 1603 at /home/aik/p/kernel/arch/powerpc/include/asm/book3s/64/kup-radix.h:145 # CPU: 0 PID: 1603 Comm: amr Not tainted 5.10.0-rc6_v5.10-rc6_a+fstn1 #24 # NIP: c00000000009ece8 LR: c00000000009ece4 CTR: 0000000000000000 # REGS: c00000000dc63560 TRAP: 0700 Not tainted (5.10.0-rc6_v5.10-rc6_a+fstn1) # MSR: 8000000000021033 CR: 28002888 XER: 20040000 # CFAR: c0000000001fa928 IRQMASK: 1 # GPR00: c00000000009ece4 c00000000dc637f0 c000000002397600 000000000000001f # GPR04: c0000000020eb318 0000000000000000 c00000000dc63494 0000000000000027 # GPR08: c00000007fe4de68 c00000000dfe9180 0000000000000000 0000000000000001 # GPR12: 0000000000002000 c0000000030a0000 0000000000000000 0000000000000000 # GPR16: 0000000000000000 0000000000000000 0000000000000000 bfffffffffffffff # GPR20: 0000000000000000 c0000000134a4020 c0000000019c2218 0000000000000fe0 # GPR24: 0000000000000000 0000000000000000 c00000000d106200 0000000040000000 # GPR28: 0000000000000000 0000000000000300 c00000000dc63910 c000000001946730 # NIP __do_page_fault+0xb38/0xde0 # LR __do_page_fault+0xb34/0xde0 # Call Trace: # __do_page_fault+0xb34/0xde0 (unreliable) # handle_page_fault+0x10/0x2c # --- interrupt: 300 at strncpy_from_user+0x290/0x440 # LR = strncpy_from_user+0x284/0x440 # strncpy_from_user+0x2f0/0x440 (unreliable) # getname_flags+0x88/0x2c0 # do_sys_openat2+0x2d4/0x5f0 # do_sys_open+0xcc/0x140 # system_call_exception+0x160/0x240 # system_call_common+0xf0/0x27c # # To fix it save/restore the AMR when replaying interrupts, and also # add a check if AMR was not blocked prior to replaying interrupts. # # Originally found by syzkaller. # # Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") # Signed-off-by: Alexey Kardashevskiy # Reviewed-by: Nicholas Piggin # [mpe: Use normal commit citation format and add full oops log to change log] # Signed-off-by: Michael Ellerman # Link: https://lore.kernel.org/r/20210202091541.36499-1-aik@ozlabs.ru # < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version # < git log --format=%s --max-count=1 006b445f18fa152c8e375abf4c68eab6d0b4afae # < make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux- randconfig KCONFIG_SEED=0x86754E2E # Added to kconfig CONFIG_STANDALONE=y # Added to kconfig CONFIG_BUILD_DOCSRC=n # Added to kconfig CONFIG_MODULE_SIG=n # Added to kconfig CONFIG_CPU_BIG_ENDIAN=n # Added to kconfig CONFIG_CPU_LITTLE_ENDIAN=y # Added to kconfig CONFIG_PPC64=y # Added to kconfig CONFIG_PPC_BOOK3E_64=n # Added to kconfig CONFIG_PPC_BOOK3S_64=y # Added to kconfig CONFIG_PPC_DISABLE_WERROR=y # Added to kconfig CONFIG_SECTION_MISMATCH_WARN_ONLY=y # Added to kconfig CONFIG_PREVENT_FIRMWARE_BUILD=y # Added to kconfig CONFIG_LD_HEAD_STUB_CATCH=y # Added to kconfig CONFIG_TRIM_UNUSED_KSYMS=n # Added to kconfig CONFIG_UBSAN=n # < make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux- help # make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux- olddefconfig .config:5453:warning: override: reassigning to symbol PPC64 .config:5456:warning: override: reassigning to symbol PPC_DISABLE_WERROR .config:5457:warning: override: reassigning to symbol SECTION_MISMATCH_WARN_ONLY .config:5458:warning: override: reassigning to symbol PREVENT_FIRMWARE_BUILD # make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux- /kisskb/src/arch/powerpc/kernel/eeh.c:1571:12: warning: 'proc_eeh_show' defined but not used [-Wunused-function] 1571 | static int proc_eeh_show(struct seq_file *m, void *v) | ^~~~~~~~~~~~~ /kisskb/src/lib/test_objagg.c: In function 'test_hints_case.constprop': /kisskb/src/lib/test_objagg.c:994:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=] 994 | } | ^ /kisskb/src/kernel/seccomp.c: In function '__seccomp_filter': /kisskb/src/kernel/seccomp.c:1287:1: error: no return statement in function returning non-void [-Werror=return-type] 1287 | } | ^ cc1: some warnings being treated as errors make[2]: *** [/kisskb/src/scripts/Makefile.build:279: kernel/seccomp.o] Error 1 make[2]: *** Waiting for unfinished jobs.... make[1]: *** [/kisskb/src/Makefile:1805: kernel] Error 2 make[1]: *** Waiting for unfinished jobs.... make: *** [Makefile:185: __sub-make] Error 2 Command 'make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux- ' returned non-zero exit status 2 # rm -rf /kisskb/build/powerpc-next-rand_randconfig+ppc64le_powerpc-gcc9 # Build took: 0:05:07.433998