# git rev-parse -q --verify b1ad106c02e19d81927b5a522167780525569490^{commit}
b1ad106c02e19d81927b5a522167780525569490
already have revision, skipping fetch
# git checkout -q -f -B kisskb b1ad106c02e19d81927b5a522167780525569490
# git clean -qxdf
# < git log -1
# commit b1ad106c02e19d81927b5a522167780525569490
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Tue Mar 3 23:28:47 2020 +1100
# 
#     powerpc/mm: Fix missing KUAP disable in flush_coherent_icache()
#     
#     We received a report of strange kernel faults which turned out to be
#     due to a missing KUAP disable in flush_coherent_icache() called
#     from flush_icache_range().
#     
#     The fault looks like:
#     
#       Kernel attempted to access user page (7fffc30d9c00) - exploit attempt? (uid: 1009)
#       BUG: Unable to handle kernel data access on read at 0x7fffc30d9c00
#       Faulting instruction address: 0xc00000000007232c
#       Oops: Kernel access of bad area, sig: 11 [#1]
#       LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
#       CPU: 35 PID: 5886 Comm: sigtramp Not tainted 5.6.0-rc2-gcc-8.2.0-00003-gfc37a1632d40 #79
#       NIP:  c00000000007232c LR: c00000000003b7fc CTR: 0000000000000000
#       REGS: c000001e11093940 TRAP: 0300   Not tainted  (5.6.0-rc2-gcc-8.2.0-00003-gfc37a1632d40)
#       MSR:  900000000280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28000884  XER: 00000000
#       CFAR: c0000000000722fc DAR: 00007fffc30d9c00 DSISR: 08000000 IRQMASK: 0
#       GPR00: c00000000003b7fc c000001e11093bd0 c0000000023ac200 00007fffc30d9c00
#       GPR04: 00007fffc30d9c18 0000000000000000 c000001e11093bd4 0000000000000000
#       GPR08: 0000000000000000 0000000000000001 0000000000000000 c000001e1104ed80
#       GPR12: 0000000000000000 c000001fff6ab380 c0000000016be2d0 4000000000000000
#       GPR16: c000000000000000 bfffffffffffffff 0000000000000000 0000000000000000
#       GPR20: 00007fffc30d9c00 00007fffc30d8f58 00007fffc30d9c18 00007fffc30d9c20
#       GPR24: 00007fffc30d9c18 0000000000000000 c000001e11093d90 c000001e1104ed80
#       GPR28: c000001e11093e90 0000000000000000 c0000000023d9d18 00007fffc30d9c00
#       NIP flush_icache_range+0x5c/0x80
#       LR  handle_rt_signal64+0x95c/0xc2c
#       Call Trace:
#         0xc000001e11093d90 (unreliable)
#         handle_rt_signal64+0x93c/0xc2c
#         do_notify_resume+0x310/0x430
#         ret_from_except_lite+0x70/0x74
#       Instruction dump:
#       409e002c 7c0802a6 3c62ff31 3863f6a0 f8010080 48195fed 60000000 48fe4c8d
#       60000000 e8010080 7c0803a6 7c0004ac <7c00ffac> 7c0004ac 4c00012c 38210070
#     
#     This path through handle_rt_signal64() to setup_trampoline() and
#     flush_icache_range() is only triggered by 64-bit processes that have
#     unmapped their VDSO, which is rare.
#     
#     flush_icache_range() takes a range of addresses to flush. In
#     flush_coherent_icache() we implement an optimisation for CPUs where we
#     know we don't actually have to flush the whole range, we just need to
#     do a single icbi.
#     
#     However we still execute the icbi on the user address of the start of
#     the range we're flushing. On CPUs that also implement KUAP (Power9)
#     that leads to the spurious fault above.
#     
#     We should be able to pass any address, including a kernel address, to
#     the icbi on these CPUs, which would avoid any interaction with KUAP.
#     But I don't want to make that change in a bug fix, just in case it
#     surfaces some strange behaviour on some CPU.
#     
#     So for now just disable KUAP around the icbi. Note the icbi is treated
#     as a load, so we allow read access, not write as you'd expect.
#     
#     Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU")
#     Cc: stable@vger.kernel.org # v5.2+
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-ld --version
# < git log --format=%s --max-count=1 b1ad106c02e19d81927b5a522167780525569490
# < make -s -j 24 ARCH=x86 O=/kisskb/build/powerpc-fixes_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  x86_64_defconfig
# < make -s -j 24 ARCH=x86 O=/kisskb/build/powerpc-fixes_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  help
# make -s -j 24 ARCH=x86 O=/kisskb/build/powerpc-fixes_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  olddefconfig
# make -s -j 24 ARCH=x86 O=/kisskb/build/powerpc-fixes_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/x86_64-linux/bin/x86_64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_x86_64_defconfig_x86_64-gcc8
# Build took: 0:03:01.800773