Buildresult: powerpc-next/s390-defconfig/s390x-gcc8 built on May 18 2019, 20:22

kisskb

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Status:	OK
Date/Time:	May 18 2019, 20:22
Duration:	0:03:37.286591
Builder:	ka4
Revision:	powerpc/64s: Use early_mmu_has_feature() in set_kuap() (`8150a153c013aa2dd1ffae43370b89ac1347a7fb)`
Target:	powerpc-next/s390-defconfig/s390x-gcc8
Branch:	powerpc-next
Compiler:	s390x-gcc8 (s390-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30)
Config:	defconfig (download)
Log:	Download original Possible warnings (4) <stdin>:1478:2: warning: #warning syscall pidfd_send_signal not implemented [-Wcpp] <stdin>:1481:2: warning: #warning syscall io_uring_setup not implemented [-Wcpp] <stdin>:1484:2: warning: #warning syscall io_uring_enter not implemented [-Wcpp] <stdin>:1487:2: warning: #warning syscall io_uring_register not implemented [-Wcpp] Full Log # git gc # git rev-parse -q --verify 8150a153c013aa2dd1ffae43370b89ac1347a7fb^{commit} 8150a153c013aa2dd1ffae43370b89ac1347a7fb already have revision, skipping fetch # git checkout -q -f -B kisskb 8150a153c013aa2dd1ffae43370b89ac1347a7fb # git clean -qxdf # < git log -1 # commit 8150a153c013aa2dd1ffae43370b89ac1347a7fb # Author: Michael Ellerman <mpe@ellerman.id.au> # Date: Wed May 8 13:06:42 2019 +1000 # # powerpc/64s: Use early_mmu_has_feature() in set_kuap() # # When implementing the KUAP support on Radix we fixed one case where # mmu_has_feature() was being called too early in boot via # __put_user_size(). # # However since then some new code in linux-next has created a new path # via which we can end up calling mmu_has_feature() too early. # # On P9 this leads to crashes early in boot if we have both PPC_KUAP and # CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG enabled. Our early boot code # calls printk() which calls probe_kernel_read(), that does a # __copy_from_user_inatomic() which calls into set_kuap() and that uses # mmu_has_feature(). # # At that point in boot we haven't patched MMU features yet so the debug # code in mmu_has_feature() complains, and calls printk(). At that point # we recurse, eg: # # ... # dump_stack+0xdc # probe_kernel_read+0x1a4 # check_pointer+0x58 # ... # printk+0x40 # dump_stack_print_info+0xbc # dump_stack+0x8 # probe_kernel_read+0x1a4 # probe_kernel_read+0x19c # check_pointer+0x58 # ... # printk+0x40 # cpufeatures_process_feature+0xc8 # scan_cpufeatures_subnodes+0x380 # of_scan_flat_dt_subnodes+0xb4 # dt_cpu_ftrs_scan_callback+0x158 # of_scan_flat_dt+0xf0 # dt_cpu_ftrs_scan+0x3c # early_init_devtree+0x360 # early_setup+0x9c # # And so on for infinity, symptom is a dead system. # # Even more fun is what happens when using the hash MMU (ie. p8 or p9 # with Radix disabled), and when we don't have # CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG enabled. With the debug disabled # we don't check if static keys have been initialised, we just rely on # the jump label. But the jump label defaults to true so we just whack # the AMR even though Radix is not enabled. # # Clearing the AMR is fine, but after we've done the user copy we write # (0b11 << 62) into AMR. When using hash that makes all pages with key # zero no longer readable or writable. All kernel pages implicitly have # key zero, and so all of a sudden the kernel can't read or write any of # its memory. Again dead system. # # In the medium term we have several options for fixing this. # probe_kernel_read() doesn't need to touch AMR at all, it's not doing a # user access after all, but it uses __copy_from_user_inatomic() just # because it's easy, we could fix that. # # It would also be safe to default to not writing to the AMR during # early boot, until we've detected features. But it's not clear that # flipping all the MMU features to static_key_false won't introduce # other bugs. # # But for now just switch to early_mmu_has_feature() in set_kuap(), that # avoids all the problems with jump labels. It adds the overhead of a # global lookup and test, but that's probably trivial compared to the # writes to the AMR anyway. # # Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") # Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> # Reviewed-by: Russell Currey <ruscur@russell.cc> # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux-ld --version # < git log --format=%s --max-count=1 8150a153c013aa2dd1ffae43370b89ac1347a7fb # < make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-next_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- defconfig # make -s -j 120 ARCH=s390 O=/kisskb/build/powerpc-next_s390-defconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- <stdin>:1478:2: warning: #warning syscall pidfd_send_signal not implemented [-Wcpp] <stdin>:1481:2: warning: #warning syscall io_uring_setup not implemented [-Wcpp] <stdin>:1484:2: warning: #warning syscall io_uring_enter not implemented [-Wcpp] <stdin>:1487:2: warning: #warning syscall io_uring_register not implemented [-Wcpp] Completed OK # rm -rf /kisskb/build/powerpc-next_s390-defconfig_s390x-gcc8 # Build took: 0:03:37.286591

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