Re: crypto: Kernel memory overwrite attempt detected to spans multiple pages

[Kees Cook]

On Wed, Mar 20, 2019 at 11:57 AM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> On Tue, Mar 19, 2019 at 10:09:13AM -0700, Eric Biggers wrote:
> > On Tue, Mar 19, 2019 at 12:54:23PM +0100, Geert Uytterhoeven wrote:
> > > When running the sha1-asm crypto selftest on arm with
> > > CONFIG_HARDENED_USERCOPY_PAGESPAN=y:
> > >
> > >     usercopy: Kernel memory overwrite attempt detected to spans
> > > multiple pages (offset 0, size 42)!
> > >     ------------[ cut here ]------------
> > >     kernel BUG at mm/usercopy.c:102!
> > >     Internal error: Oops - BUG: 0 [#1] SMP ARM
> > >     Modules linked in:
> > >     CPU: 0 PID: 35 Comm: cryptomgr_test Not tainted
> > > 5.1.0-rc1-koelsch-01109-gbeb7d6376ecfbf07-dirty #397
> > >     Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
> > >     PC is at usercopy_abort+0x68/0x90
> > >     LR is at usercopy_abort+0x68/0x90
> > >     pc : [<c030fd60>]    lr : [<c030fd60>]    psr: 60000013
> > >     sp : ea54bc60  ip : 00000010  fp : cccccccd
> > >     r10: 00000000  r9 : c0e0ce04  r8 : ea54d009
> > >     r7 : ea54d00a  r6 : 00000000  r5 : 0000002a  r4 : c09d1120
> > >     r3 : dd6cd422  r2 : dd6cd422  r1 : 2abb4000  r0 : 0000005f
> > >     Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
> > >     Control: 30c5387d  Table: 40003000  DAC: fffffffd
> > >     Process cryptomgr_test (pid: 35, stack limit = 0x(ptrval))
> > >     Stack: (0xea54bc60 to 0xea54c000)
> > >     bc60: c09d1120 c09d1120 c09d1120 00000000 0000002a 0000002a
> > > 00000000 c0310060
> > >     bc80: 0000002a 00000000 000001c0 00000000 00000000 c0eb11e8
> > > ea54cfe0 ea538c00
> > >     bca0: 00000000 ea54cfe0 ebef73e0 0000002a ea538c20 ea54bd84
> > > 0000003a c0427a30
> > >     bcc0: ea54bdbc 00000000 00000000 c081cf70 eb074280 c081cf70
> > > 0000002a c081cf80
> > >     bce0: 0000000e c07da138 ea54bd0c 00000000 c084061c c04248e8
> > > c0e0a408 eb074240
> > >     bd00: eb074200 c04253c8 eb074280 ea550000 00000012 dd6cd422
> > > ebef7480 eb074200
> > >     bd20: ea54bd84 c081cf64 ea537200 00000002 00000000 00000014
> > > c084061c c0428c38
> > >     bd40: ea54bd84 ea54bdbc c081cd34 00000000 c0e4e4b4 ea538c40
> > > 00000002 eabe4e80
> > >     bd60: ea538c00 00000400 ea4f7a00 ea4f7a60 eb074240 00000060
> > > 00000006 c09d544c
> > >     bd80: 00000038 00000003 00000000 00000038 ea54bd7c 00000001
> > > eb074200 00000000
> > >     bda0: 00000000 dead4ead ffffffff ffffffff ea54bdb0 ea54bdb0
> > > 00000000 c081cf70
> > >     bdc0: c081ce68 c081ce78 ea4f7480 eb000780 00000dc0 eb000780
> > > c0e4ee80 443e9884
> > >     bde0: 6ed23b1c a14aaeba e52951f9 f17046e5 fefefefe fefefefe
> > > fefefefe fefefefe
> > >     be00: eb000780 c04292c4 c0e0a638 60000013 60000013 c0305298
> > > ea4f7a00 c03062bc
> > >     be20: eb000780 00000cc0 ea4f7a00 dd6cd422 00000cc0 ea538c00
> > > 00000002 eabe4e40
> > >     be40: ea537200 00000007 00000000 ea4f7a00 eb074200 c0429314
> > > eb074200 ea538c00
> > >     be60: ea4f7a00 0000000a eabe4e80 c084061c c08405fc 00000006
> > > c04dace8 00000006
> > >     be80: 00000000 c084065c ea537200 0000000e 00000400 eb04de08
> > > ea4f71a8 c0429420
> > >     bea0: 00000400 ea537200 0000000e ea537200 0000000e c0429374
> > > 00000400 ffffffff
> > >     bec0: 000000a2 c042a414 00000103 c0e0a408 00000000 c0e0a438
> > > c0e5a2a0 c0e5a2a0
> > >     bee0: 00000001 00000001 00000017 ffffe000 00000000 60000013
> > > c0e5a2a0 c0269470
> > >     bf00: c09c9ed0 ea54bf5c 00000103 00000000 00000000 c0e0a408
> > > ea537280 0000000e
> > >     bf20: 00000400 c0426500 00000000 eb04de08 ea4f71a8 c02694f4
> > > c09c9ed0 ea54bf5c
> > >     bf40: ea54bf28 c02699d0 ea54bf5c dd6cd422 ea537200 dd6cd422
> > > c09c9ed0 ea537200
> > >     bf60: ea4af1c0 ea54a000 ea537200 c0426500 00000000 eb04de08
> > > ea4f71a8 c0426524
> > >     bf80: ea4f7180 c023dcec ea54a000 ea4af1c0 c023dbb4 00000000
> > > 00000000 00000000
> > >     bfa0: 00000000 00000000 00000000 c02010d8 00000000 00000000
> > > 00000000 00000000
> > >     bfc0: 00000000 00000000 00000000 00000000 00000000 00000000
> > > 00000000 00000000
> > >     bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > > 00000000 00000000
> > >     [<c030fd60>] (usercopy_abort) from [<c0310060>]
> > > (__check_object_size+0x2d8/0x448)
> > >     [<c0310060>] (__check_object_size) from [<c0427a30>]
> > > (build_test_sglist+0x268/0x2d8)
> > >     [<c0427a30>] (build_test_sglist) from [<c0428c38>]
> > > (test_hash_vec_cfg+0x110/0x694)
> > >     [<c0428c38>] (test_hash_vec_cfg) from [<c0429314>]
> > > (__alg_test_hash+0x158/0x1b8)
> > >     [<c0429314>] (__alg_test_hash) from [<c0429420>] (alg_test_hash+0xac/0xf4)
> > >     [<c0429420>] (alg_test_hash) from [<c042a414>] (alg_test.part.4+0x264/0x2f8)
> > >     [<c042a414>] (alg_test.part.4) from [<c0426524>] (cryptomgr_test+0x24/0x44)
> > >     [<c0426524>] (cryptomgr_test) from [<c023dcec>] (kthread+0x138/0x150)
> > >     [<c023dcec>] (kthread) from [<c02010d8>] (ret_from_fork+0x14/0x3c)
> > >     Exception stack(0xea54bfb0 to 0xea54bff8)
> > >     bfa0:                                     00000000 00000000
> > > 00000000 00000000
> > >     bfc0: 00000000 00000000 00000000 00000000 00000000 00000000
> > > 00000000 00000000
> > >     bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > >     Code: e58de000 e98d0012 e1a0100c ebfd6712 (e7f001f2)
> > >     ---[ end trace 190b3cf48e720f78 ]---
> > >     BUG: sleeping function called from invalid context at
> > > include/linux/percpu-rwsem.h:34
> > >     in_atomic(): 0, irqs_disabled(): 128, pid: 35, name: cryptomgr_test
> > >     CPU: 0 PID: 35 Comm: cryptomgr_test Tainted: G      D
> > > 5.1.0-rc1-koelsch-01109-gbeb7d6376ecfbf07-dirty #397
> > >     Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
> > >     [<c020ec74>] (unwind_backtrace) from [<c020ae58>] (show_stack+0x10/0x14)
> > >     [<c020ae58>] (show_stack) from [<c07c3624>] (dump_stack+0x7c/0x9c)
> > >     [<c07c3624>] (dump_stack) from [<c0242e14>] (___might_sleep+0xf4/0x158)
> > >     [<c0242e14>] (___might_sleep) from [<c0230210>] (exit_signals+0x2c/0x258)
> > >     [<c0230210>] (exit_signals) from [<c0223d6c>] (do_exit+0x114/0xa20)
> > >     [<c0223d6c>] (do_exit) from [<c020b160>] (die+0x304/0x344)
> > >     [<c020b160>] (die) from [<c020b388>] (do_undefinstr+0x80/0x190)
> > >     [<c020b388>] (do_undefinstr) from [<c0201b24>] (__und_svc_finish+0x0/0x3c)
> > >     Exception stack(0xea54bc10 to 0xea54bc58)
> > >     bc00:                                     0000005f 2abb4000
> > > dd6cd422 dd6cd422
> > >     bc20: c09d1120 0000002a 00000000 ea54d00a ea54d009 c0e0ce04
> > > 00000000 cccccccd
> > >     bc40: 00000010 ea54bc60 c030fd60 c030fd60 60000013 ffffffff
> > >     [<c0201b24>] (__und_svc_finish) from [<c030fd60>] (usercopy_abort+0x68/0x90)
> > >     [<c030fd60>] (usercopy_abort) from [<c0310060>]
> > > (__check_object_size+0x2d8/0x448)
> > >     [<c0310060>] (__check_object_size) from [<c0427a30>]
> > > (build_test_sglist+0x268/0x2d8)
> > >     [<c0427a30>] (build_test_sglist) from [<c0428c38>]
> > > (test_hash_vec_cfg+0x110/0x694)
> > >     [<c0428c38>] (test_hash_vec_cfg) from [<c0429314>]
> > > (__alg_test_hash+0x158/0x1b8)
> > >     [<c0429314>] (__alg_test_hash) from [<c0429420>] (alg_test_hash+0xac/0xf4)
> > >     [<c0429420>] (alg_test_hash) from [<c042a414>] (alg_test.part.4+0x264/0x2f8)
> > >     [<c042a414>] (alg_test.part.4) from [<c0426524>] (cryptomgr_test+0x24/0x44)
> > >     [<c0426524>] (cryptomgr_test) from [<c023dcec>] (kthread+0x138/0x150)
> > >     [<c023dcec>] (kthread) from [<c02010d8>] (ret_from_fork+0x14/0x3c)
> > >     Exception stack(0xea54bfb0 to 0xea54bff8)
> > >     bfa0:                                     00000000 00000000
> > > 00000000 00000000
> > >     bfc0: 00000000 00000000 00000000 00000000 00000000 00000000
> > > 00000000 00000000
> > >     bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > >
> >
> > Well, this must happen with the new (in 5.1) crypto self-tests implementation
> > for any crypto algorithm when CONFIG_HARDENED_USERCOPY_PAGESPAN=y.  I don't
> > understand why hardened usercopy considers it a bug though, as there's no buffer
> > overflow.  The crypto tests use copy_from_iter() to copy data into a 2-page
> > buffer that was allocated with __get_free_pages():
> >
> >       __get_free_pages(GFP_KERNEL, 1)
> >
> > ... where 1 means an order-1 allocation.
> >
> > If it copies to offset=4064 len=42, for example, then hardened usercopy
> > considers it a bug even though the buffer is 8192 bytes long.  Why?
> >
> > It isn't actually copying anything to/from userspace, BTW; it's using iov_iter
> > with ITER_KVEC.
> >
> > - Eric
>
> Kees, any thoughts on why hardened usercopy rejects copies spanning a page
> boundary when they seem to be fine?

This is due to missing the compound page marking, if I remember
correctly. However, I tend to leave the pagespan test disabled: it
really isn't ready for production use -- there are a lot of missing
annotations still.

-- 
Kees Cook