On Friday, February 1, 2019 4:43:52 PM IST Michael Ellerman wrote: > Michael Ellerman <m...@ellerman.id.au> writes: > > > Adding Simon who wrote the code. > > > > Chandan Rajendra <chan...@linux.ibm.com> writes: > >> When executing fstests' generic/026 test, I hit the following call trace, > >> > >> [ 417.061038] BUG: Unable to handle kernel data access at > >> 0xc00000062ac40000 > >> [ 417.062172] Faulting instruction address: 0xc000000000092240 > >> [ 417.062242] Oops: Kernel access of bad area, sig: 11 [#1] > >> [ 417.062299] LE SMP NR_CPUS=2048 DEBUG_PAGEALLOC NUMA pSeries > >> [ 417.062366] Modules linked in: > >> [ 417.062401] CPU: 0 PID: 27828 Comm: chacl Not tainted > >> 5.0.0-rc2-next-20190115-00001-g6de6dba64dda #1 > >> [ 417.062495] NIP: c000000000092240 LR: c00000000066a55c CTR: > >> 0000000000000000 > >> [ 417.062567] REGS: c00000062c0c3430 TRAP: 0300 Not tainted > >> (5.0.0-rc2-next-20190115-00001-g6de6dba64dda) > >> [ 417.062660] MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: > >> 44000842 XER: 20000000 > >> [ 417.062750] CFAR: 00007fff7f3108ac DAR: c00000062ac40000 DSISR: > >> 40000000 IRQMASK: 0 > >> GPR00: 0000000000000000 c00000062c0c36c0 c0000000017f4c00 > >> c00000000121a660 > >> GPR04: c00000062ac3fff9 0000000000000004 0000000000000020 > >> 00000000275b19c4 > >> GPR08: 000000000000000c 46494c4500000000 5347495f41434c5f > >> c0000000026073a0 > >> GPR12: 0000000000000000 c0000000027a0000 0000000000000000 > >> 0000000000000000 > >> GPR16: 0000000000000000 0000000000000000 0000000000000000 > >> 0000000000000000 > >> GPR20: c00000062ea70020 c00000062c0c38d0 0000000000000002 > >> 0000000000000002 > >> GPR24: c00000062ac3ffe8 00000000275b19c4 0000000000000001 > >> c00000062ac30000 > >> GPR28: c00000062c0c38d0 c00000062ac30050 c00000062ac30058 > >> 0000000000000000 > >> [ 417.063563] NIP [c000000000092240] memcmp+0x120/0x690 > >> [ 417.063635] LR [c00000000066a55c] xfs_attr3_leaf_lookup_int+0x53c/0x5b0 > >> [ 417.063709] Call Trace: > >> [ 417.063744] [c00000062c0c36c0] [c00000000066a098] > >> xfs_attr3_leaf_lookup_int+0x78/0x5b0 (unreliable) > >> [ 417.063851] [c00000062c0c3760] [c000000000693f8c] > >> xfs_da3_node_lookup_int+0x32c/0x5a0 > >> [ 417.063944] [c00000062c0c3820] [c0000000006634a0] > >> xfs_attr_node_addname+0x170/0x6b0 > >> [ 417.064034] [c00000062c0c38b0] [c000000000664ffc] > >> xfs_attr_set+0x2ac/0x340 > >> [ 417.064118] [c00000062c0c39a0] [c000000000758d40] > >> __xfs_set_acl+0xf0/0x230 > >> [ 417.064190] [c00000062c0c3a00] [c000000000758f50] xfs_set_acl+0xd0/0x160 > >> [ 417.064268] [c00000062c0c3aa0] [c0000000004b69b0] > >> set_posix_acl+0xc0/0x130 > >> [ 417.064339] [c00000062c0c3ae0] [c0000000004b6a88] > >> posix_acl_xattr_set+0x68/0x110 > >> [ 417.064412] [c00000062c0c3b20] [c0000000004532d4] > >> __vfs_setxattr+0xa4/0x110 > >> [ 417.064485] [c00000062c0c3b80] [c000000000454c2c] > >> __vfs_setxattr_noperm+0xac/0x240 > >> [ 417.064566] [c00000062c0c3bd0] [c000000000454ee8] > >> vfs_setxattr+0x128/0x130 > >> [ 417.064638] [c00000062c0c3c30] [c000000000455138] setxattr+0x248/0x600 > >> [ 417.064710] [c00000062c0c3d90] [c000000000455738] > >> path_setxattr+0x108/0x120 > >> [ 417.064785] [c00000062c0c3e00] [c000000000455778] sys_setxattr+0x28/0x40 > >> [ 417.064858] [c00000062c0c3e20] [c00000000000bae4] system_call+0x5c/0x70 > >> [ 417.064930] Instruction dump: > >> [ 417.064964] 7d201c28 7d402428 7c295040 38630008 38840008 408201f0 > >> 4200ffe8 2c050000 > >> [ 417.065051] 4182ff6c 20c50008 54c61838 7d201c28 <7d402428> 7d293436 > >> 7d4a3436 7c295040 > >> [ 417.065150] ---[ end trace 0d060411b5e3741b ]--- > >> > >> > >> Both the memory locations passed to memcmp() had "SGI_ACL_FILE" and len > >> argument of memcmp() was set to 12. s1 argument of memcmp() had the value > >> 0x00000000f4af0485, while s2 argument had the value 0x00000000ce9e316f. > >> > >> The following is the code path within memcmp() that gets executed for the > >> above mentioned values, > >> > >> - Since len (i.e. 12) is greater than 7, we branch to .Lno_short. > >> - We then prefetch the contents of r3 & r4 and branch to > >> .Ldiffoffset_8bytes_make_align_start. > >> - Under .Ldiffoffset_novmx_cmp, Since r3 is unaligned we end up comparing > >> "SGI" part of the string. r3's value is then aligned. r4's value is > >> incremented by 3. For comparing the remaining 9 bytes, we jump to > >> .Lcmp_lt32bytes. > >> - Here, 8 bytes of the remaining 9 bytes are compared and execution moves > >> to > >> .Lcmp_rest_lt8bytes. > >> - Here we execute "LD rB,0,r4". In the case of this bug, r4 has an > >> unaligned > >> value and hence ends up accessing the "next" double word. The "next" > >> double > >> word happens to occur after the last page mapped into the kernel's > >> address > >> space and hence this leads to the previously listed oops. > > > > Thanks for the analysis. > > > > This is just a bug, we can't read past the end of the source or dest. > > How about this, works for me. > > cheers > > diff --git a/arch/powerpc/lib/memcmp_64.S b/arch/powerpc/lib/memcmp_64.S > index 844d8e774492..2a302158cb53 100644 > --- a/arch/powerpc/lib/memcmp_64.S > +++ b/arch/powerpc/lib/memcmp_64.S > @@ -215,20 +215,29 @@ _GLOBAL_TOC(memcmp) > beq .Lzero > > .Lcmp_rest_lt8bytes: > - /* Here we have only less than 8 bytes to compare with. at least s1 > - * Address is aligned with 8 bytes. > - * The next double words are load and shift right with appropriate > - * bits. > + /* > + * Here we have less than 8 bytes left to compare with. We mustn't read > + * past the end of either source or dest. > */ > - subfic r6,r5,8 > - slwi r6,r6,3 > - LD rA,0,r3 > - LD rB,0,r4 > - srd rA,rA,r6 > - srd rB,rB,r6 > - cmpld cr0,rA,rB > + > + /* If we have less than 4 bytes, just do byte at a time */ > + cmpwi cr1, r5, 4 > + blt cr1, .Lshort > + > + /* Compare 4 bytes */ > + LW rA,0,r3 > + LW rB,0,r4 > + cmpd cr0,rA,rB > bne cr0,.LcmpAB_lightweight > - b .Lzero > + > + /* If we had exactly 4 bytes left, we're done now */ > + beq cr1, .Lzero > + > + /* Otherwise do what ever's left a byte at a time */ > + subi r5, r5, 4 > + addi r3, r3, 4 > + addi r4, r4, 4 > + b .Lshort > > .Lnon_zero: > mr r3,rC > >
With the above patch, Linux kernel does not end up in oops. Hence, Tested-by: Chandan Rajendra <chan...@linux.ibm.com> -- chandan