On Thu, 23 Apr 2020, Gerald Schaefer wrote: > On Wed, 22 Apr 2020 14:46:05 -0500 > Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > On Wed, Apr 22, 2020 at 05:21:26PM +0200, Gerald Schaefer wrote: > > > > Sorry, just noticed this. Heiko will return next month, and I'm not > > > > really familiar with s390 livepatching. Adding Vasily, he might > > > > have some more insight. > > > > > > > > So, I might be completely wrong here, but using s390_kernel_write() > > > > for writing to anything other than 1:1 mapped kernel, should go > > > > horribly wrong, as that runs w/o DAT. It would allow to bypass > > > > DAT write protection, which I assume is why you want to use it, > > > > but it should not work on module text section, as that would be > > > > in vmalloc space and not 1:1 mapped kernel memory. > > > > > > > > Not quite sure how to test / trigger this, did this really work for > > > > you on s390? > > > > > > OK, using s390_kernel_write() as default write function for module > > > relocation seems to work fine for me, so apparently I am missing / > > > mixing up something. Sorry for the noise, please ignore my concern. > > > > Hi Gerald, > > > > I think you were right. Joe found the below panic with his klp-convert > > tests. > > > > Your test was probably the early module loading case (normal relocations > > before write protection), rather than the late case. Not sure why that > > would work, but calling s390_kernel_write() late definitely seems to be > > broken. > > > > Is there some other way to write vmalloc'ed s390 text without using > > module_disable_ro()? > > > > [ 50.294476] Unable to handle kernel pointer dereference in virtual kernel address space > > [ 50.294479] Failing address: 000003ff8015b000 TEID: 000003ff8015b407 > > [ 50.294480] Fault in home space mode while using kernel ASCE. > > [ 50.294483] AS:000000006cef0007 R3:000000007e2c4007 S:0000000003ccb800 P:0000 00000257321d > > [ 50.294557] Oops: 0004 ilc:3 [#1] SMP > > [ 50.294561] Modules linked in: test_klp_convert1(K+) test_klp_convert_mod ghash_s390 prng xts aes_s390 des_s390 libdes sha512_s390 vmur zcrypt_cex4 ip_tables xfs libcrc32c dasd_fba_mod qeth_l2 dasd_eckd_mod dasd_mod qeth lcs ctcm qdio cc > > wgroup fsm dm_mirror dm_region_hash dm_log dm_mod pkey zcrypt [last unloaded: test_klp_atomic_replace] > > [ 50.294576] CPU: 0 PID: 1743 Comm: modprobe Tainted: G K 5.6.0 + #2 > > [ 50.294579] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0) > > [ 50.294583] Krnl PSW : 0704e00180000000 000000006bf6be0a (apply_rela+0x2ba/0x 4e0) > > [ 50.294589] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI: 0 EA:3 > > [ 50.294684] Krnl GPRS: 000003ff80147010 000003e0001b9588 000003ff8015c168 000 003ff8015b19a > > [ 50.294686] 000003ff8015b07c 0d10e310100a0004 000003ff80147010 000 00000000000a0 > > [ 50.294687] 000003ff8015e588 000003ff8015e5e8 000003ff8015d300 000 0003b00000014 > > [ 50.294698] 000000007a663000 000000006c6bbb80 000003e0009a7918 000 003e0009a78b8 > > [ 50.294707] Krnl Code: 000000006bf6bdf8: e350d0080004 lg %r5,8(%r 13) > > [ 50.294707] 000000006bf6bdfe: e34010080008 ag %r4,8(%r 1) > > [ 50.294707] #000000006bf6be04: e340a2000008 ag %r4,512( %r10) > > [ 50.294707] >000000006bf6be0a: e35040000024 stg %r5,0(%r 4) > > [ 50.294707] 000000006bf6be10: c050007c6136 larl %r5,0000 00006cef807c > > [ 50.294707] 000000006bf6be16: e35050000012 lt %r5,0(%r 5) > > [ 50.294707] 000000006bf6be1c: a78400a6 brc 8,000000 006bf6bf68 > > [ 50.294707] 000000006bf6be20: a55e07f1 llilh %r5,2033 > > 01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP stop from CPU 01. > > 01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP stop from CPU 00. > > [ 50.295369] Call Trace: > > [ 50.295372] [<000000006bf6be0a>] apply_rela+0x2ba/0x4e0 > > [ 50.295376] [<000000006bf6c5c8>] apply_relocate_add+0xe0/0x138 > > [ 50.295378] [<000000006c0229a0>] klp_apply_section_relocs+0xe8/0x128 > > [ 50.295380] [<000000006c022b4c>] klp_apply_object_relocs+0x9c/0xd0 > > [ 50.295382] [<000000006c022bb0>] klp_init_object_loaded+0x30/0x138 > > [ 50.295384] [<000000006c023052>] klp_enable_patch+0x39a/0x870 > > [ 50.295387] [<000003ff8015b0da>] test_klp_convert_init+0x22/0x50 [test_klp_convert1] > > [ 50.295389] [<000000006bf54838>] do_one_initcall+0x40/0x1f0 > > [ 50.295391] [<000000006c04d610>] do_init_module+0x70/0x280 > > [ 50.295392] [<000000006c05002a>] load_module+0x1aba/0x1d10 > > [ 50.295394] [<000000006c0504c4>] __do_sys_finit_module+0xa4/0xe8 > > [ 50.295416] [<000000006c6b5742>] system_call+0x2aa/0x2c8 > > [ 50.295416] Last Breaking-Event-Address: > > [ 50.295418] [<000000006c6b6aa0>] __s390_indirect_jump_r4+0x0/0xc > > [ 50.295421] Kernel panic - not syncing: Fatal exception: panic_on_oops > > > > Hi Josh, > > this is strange. While I would have expected an exception similar to > this, it really should have happened on the "sturg" instruction which > does the DAT-off store in s390_kernel_write(), and certainly not with > an ID of 0004 (protection). However, in your case, it happens on a > normal store instruction, with 0004 indicating a protection exception. > > This is more like what I would expect e.g. in the case where you do > _not_ use the s390_kernel_write() function for RO module text patching, > but rather normal memory access. So I am pretty sure that this is not > related to the s390_kernel_write(), but some other issue, maybe some > place left where you still use normal memory access? The call trace above also suggests that it is not a late relocation, no? The path is from KLP module init function through klp_enable_patch. It should mean that the to-be-patched object is loaded (it must be a module thanks to a check klp_init_object_loaded(), vmlinux relocations were processed earlier in apply_relocations()). However, the KLP module state here must be COMING, so s390_kernel_write() should be used. What are we missing? Joe, could you debug this a bit, please? > There is also some good news. While thinking about how to use "sturg" > for vmalloc addresses, I came up with the idea to use "lra" (load > real address) before that. Then I found out that we already do exactly > that in the inline assembly, so all should be fine. Well, maybe the > comment for s390_kernel_write() could be improved... > > Vasily also found out that we apparently already use s390_kernel_write() > for module text, for alternatives, so I guess we can safely assume that > it should work fine in principle. Phew, okay. I noticed that s390_kernel_write() is called on a couple of places already (kprobes) and I wondered where the trick was. Thanks Miroslav
