# git rev-parse -q --verify 8a17ea07703f5f41e8c96b123f63be4eac107374^{commit} 8a17ea07703f5f41e8c96b123f63be4eac107374 already have revision, skipping fetch # git checkout -q -f -B kisskb 8a17ea07703f5f41e8c96b123f63be4eac107374 # git clean -qxdf # < git log -1 # commit 8a17ea07703f5f41e8c96b123f63be4eac107374 # Author: Aneesh Kumar K.V # Date: Wed Jan 8 11:14:22 2020 +0530 # # powerpc/mm/hash: Fix sharing context ids between kernel & userspace # # Commit 0034d395f89d ("powerpc/mm/hash64: Map all the kernel regions in # the same 0xc range") has a bug in the definition of MIN_USER_CONTEXT. # # The result is that the context id used for the vmemmap and the lowest # context id handed out to userspace are the same. The context id is # essentially the process identifier as far as the first stage of the # MMU translation is concerned. # # This can result in multiple SLB entries with the same VSID (Virtual # Segment ID), accessible to the kernel and some random userspace # process that happens to get the overlapping id, which is not expected # eg: # # 07 c00c000008000000 40066bdea7000500 1T ESID= c00c00 VSID= 66bdea7 LLP:100 # 12 0002000008000000 40066bdea7000d80 1T ESID= 200 VSID= 66bdea7 LLP:100 # # Even though the user process and the kernel use the same VSID, the # permissions in the hash page table prevent the user process from # reading or writing to any kernel mappings. # # It can also lead to SLB entries with different base page size # encodings (LLP), eg: # # 05 c00c000008000000 00006bde0053b500 256M ESID=c00c00000 VSID= 6bde0053b LLP:100 # 09 0000000008000000 00006bde0053bc80 256M ESID= 0 VSID= 6bde0053b LLP: 0 # # Such SLB entries can result in machine checks, eg. as seen on a G5: # # Oops: Machine check, sig: 7 [#1] # BE PAGE SIZE=64K MU-Hash SMP NR_CPUS=4 NUMA Power Mac # NIP: c00000000026f248 LR: c000000000295e58 CTR: 0000000000000000 # REGS: c0000000erfd3d70 TRAP: 0200 Tainted: G M (5.5.0-rcl-gcc-8.2.0-00010-g228b667d8ea1) # MSR: 9000000000109032 CR: 24282048 XER: 00000000 # DAR: c00c000000612c80 DSISR: 00000400 IRQMASK: 0 # ... # NIP [c00000000026f248] .kmem_cache_free+0x58/0x140 # LR [c088000008295e58] .putname 8x88/0xa # Call Trace: # .putname+0xB8/0xa # .filename_lookup.part.76+0xbe/0x160 # .do_faccessat+0xe0/0x380 # system_call+0x5c/ex68 # # This happens with 256MB segments and 64K pages, as the duplicate VSID # is hit with the first vmemmap segment and the first user segment, and # older 32-bit userspace maps things in the first user segment. # # On other CPUs a machine check is not seen. Instead the userspace # process can get stuck continuously faulting, with the fault never # properly serviced, due to the kernel not understanding that there is # already a HPTE for the address but with inaccessible permissions. # # On machines with 1T segments we've not seen the bug hit other than by # deliberately exercising it. That seems to be just a matter of luck # though, due to the typical layout of the user virtual address space # and the ranges of vmemmap that are typically populated. # # To fix it we add 2 to MIN_USER_CONTEXT. This ensures the lowest # context given to userspace doesn't overlap with the VMEMMAP context, # or with the context for INVALID_REGION_ID. Also add some # BUILD_BUG_ON()'s to check the values. # # Fixes: 0034d395f89d ("powerpc/mm/hash64: Map all the kernel regions in the same 0xc range") # Cc: stable@vger.kernel.org # v5.2+ # Reported-by: Christian Marillat # Reported-by: Romain Dolbeau # Signed-off-by: Aneesh Kumar K.V # [mpe: Account for INVALID_REGION_ID, mostly rewrite change log] # Signed-off-by: Michael Ellerman # < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version # < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-ld --version # < git log --format=%s --max-count=1 8a17ea07703f5f41e8c96b123f63be4eac107374 # < make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- ppc64_defconfig # make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- /kisskb/src/arch/powerpc/mm/book3s64/hash_utils.c: In function 'hash__early_init_mmu': /kisskb/src/arch/powerpc/mm/book3s64/hash_utils.c:1012:2: error: call to '__compiletime_assert_1012' declared with attribute error: BUILD_BUG_ON failed: get_kernel_context(H_VMEMMAP_END - 1) >= MIN_USER_CONTEXT /kisskb/src/arch/powerpc/mm/book3s64/hash_utils.c:1013:2: error: call to '__compiletime_assert_1013' declared with attribute error: BUILD_BUG_ON failed: get_kernel_context(PAGE_OFFSET) >= MIN_USER_CONTEXT /kisskb/src/arch/powerpc/mm/book3s64/hash_utils.c:1014:2: error: call to '__compiletime_assert_1014' declared with attribute error: BUILD_BUG_ON failed: get_kernel_context(PAGE_OFFSET - 1) >= MIN_USER_CONTEXT /kisskb/src/arch/powerpc/mm/book3s64/hash_utils.c:1015:2: error: call to '__compiletime_assert_1015' declared with attribute error: BUILD_BUG_ON failed: get_kernel_context(0xdULL << 60) >= MIN_USER_CONTEXT make[4]: *** [/kisskb/src/scripts/Makefile.build:266: arch/powerpc/mm/book3s64/hash_utils.o] Error 1 make[4]: *** Waiting for unfinished jobs.... make[3]: *** [/kisskb/src/scripts/Makefile.build:503: arch/powerpc/mm/book3s64] Error 2 make[2]: *** [/kisskb/src/scripts/Makefile.build:503: arch/powerpc/mm] Error 2 make[2]: *** Waiting for unfinished jobs.... /kisskb/src/mm/hugetlb.c: In function 'alloc_pool_huge_page': /kisskb/src/mm/hugetlb.c:1377:5: warning: 'page' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/ext4/extents.c: In function 'ext4_convert_unwritten_io_end_vec': /kisskb/src/fs/ext4/extents.c:5054:23: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl': /kisskb/src/kernel/printk/printk.c:204:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] make[1]: *** [/kisskb/src/Makefile:1693: arch/powerpc] Error 2 make[1]: *** Waiting for unfinished jobs.... /kisskb/src/fs/nfsd/nfs4xdr.c: In function 'nfsd4_encode_components_esc': /kisskb/src/fs/nfsd/nfs4xdr.c:2076:9: warning: 'str' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c: In function 'proc_reg_open': /kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c:338:21: note: 'pdeo' was declared here /kisskb/src/fs/udf/unicode.c: In function 'udf_name_conv_char': /kisskb/src/fs/udf/unicode.c:132:8: warning: 'c' may be used uninitialized in this function [-Wuninitialized] make: *** [Makefile:179: sub-make] Error 2 Command 'make -s -j 24 ARCH=powerpc O=/kisskb/build/powerpc-fixes_ppc64_defconfig_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- ' returned non-zero exit status 2 # rm -rf /kisskb/build/powerpc-fixes_ppc64_defconfig_powerpc-gcc4.6 # Build took: 0:01:20.555157