# git rev-parse -q --verify 5d2e5dd5849b4ef5e8ec35e812cdb732c13cd27e^{commit} 5d2e5dd5849b4ef5e8ec35e812cdb732c13cd27e already have revision, skipping fetch # git checkout -q -f -B kisskb 5d2e5dd5849b4ef5e8ec35e812cdb732c13cd27e # git clean -qxdf # < git log -1 # commit 5d2e5dd5849b4ef5e8ec35e812cdb732c13cd27e # 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. # # 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 # Link: https://lore.kernel.org/r/20200123102547.11623-1-mpe@ellerman.id.au # < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version # < git log --format=%s --max-count=1 5d2e5dd5849b4ef5e8ec35e812cdb732c13cd27e # < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_85xx_xes_mpc85xx_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux- 85xx/xes_mpc85xx_defconfig # make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_85xx_xes_mpc85xx_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux- /kisskb/src/drivers/mtd/nand/raw/fsl_upm.c: In function 'fun_wait_rnb': /kisskb/src/drivers/mtd/nand/raw/fsl_upm.c:65:20: warning: unused variable 'mtd' [-Wunused-variable] struct mtd_info *mtd = nand_to_mtd(&fun->chip); ^ INFO: Uncompressed kernel (size 0x8514c8) overlaps the address of the wrapper(0x400000) INFO: Fixing the link_address of wrapper to (0x900000) Image Name: Linux-5.5.0-rc3-g5d2e5dd5849b Created: Fri Jan 24 01:02:10 2020 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 4376434 Bytes = 4273.86 KiB = 4.17 MiB Load Address: 00000000 Entry Point: 00000000 Completed OK # rm -rf /kisskb/build/powerpc-fixes_85xx_xes_mpc85xx_defconfig_powerpc-gcc5 # Build took: 0:01:22.717208