Messages in this thread | | | Subject | Re: [RFC PATCH v1] powerpc: Enable KFENCE for PPC32 | From | Christophe Leroy <> | Date | Wed, 3 Mar 2021 11:31:55 +0100 |
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Le 02/03/2021 à 10:53, Marco Elver a écrit : > On Tue, 2 Mar 2021 at 10:27, Christophe Leroy > <christophe.leroy@csgroup.eu> wrote: >> Le 02/03/2021 à 10:21, Alexander Potapenko a écrit : >>>> [ 14.998426] BUG: KFENCE: invalid read in finish_task_switch.isra.0+0x54/0x23c >>>> [ 14.998426] >>>> [ 15.007061] Invalid read at 0x(ptrval): >>>> [ 15.010906] finish_task_switch.isra.0+0x54/0x23c >>>> [ 15.015633] kunit_try_run_case+0x5c/0xd0 >>>> [ 15.019682] kunit_generic_run_threadfn_adapter+0x24/0x30 >>>> [ 15.025099] kthread+0x15c/0x174 >>>> [ 15.028359] ret_from_kernel_thread+0x14/0x1c >>>> [ 15.032747] >>>> [ 15.034251] CPU: 0 PID: 111 Comm: kunit_try_catch Tainted: G B >>>> 5.12.0-rc1-s3k-dev-01534-g4f14ae75edf0-dirty #4674 >>>> [ 15.045811] ================================================================== >>>> [ 15.053324] # test_invalid_access: EXPECTATION FAILED at mm/kfence/kfence_test.c:636 >>>> [ 15.053324] Expected report_matches(&expect) to be true, but is false >>>> [ 15.068359] not ok 21 - test_invalid_access >>> >>> The test expects the function name to be test_invalid_access, i. e. >>> the first line should be "BUG: KFENCE: invalid read in >>> test_invalid_access". >>> The error reporting function unwinds the stack, skips a couple of >>> "uninteresting" frames >>> (https://elixir.bootlin.com/linux/v5.12-rc1/source/mm/kfence/report.c#L43) >>> and uses the first "interesting" one frame to print the report header >>> (https://elixir.bootlin.com/linux/v5.12-rc1/source/mm/kfence/report.c#L226). >>> >>> It's strange that test_invalid_access is missing altogether from the >>> stack trace - is that expected? >>> Can you try printing the whole stacktrace without skipping any frames >>> to see if that function is there? >>> >> >> Booting with 'no_hash_pointers" I get the following. Does it helps ? >> >> [ 16.837198] ================================================================== >> [ 16.848521] BUG: KFENCE: invalid read in finish_task_switch.isra.0+0x54/0x23c >> [ 16.848521] >> [ 16.857158] Invalid read at 0xdf98800a: >> [ 16.861004] finish_task_switch.isra.0+0x54/0x23c >> [ 16.865731] kunit_try_run_case+0x5c/0xd0 >> [ 16.869780] kunit_generic_run_threadfn_adapter+0x24/0x30 >> [ 16.875199] kthread+0x15c/0x174 >> [ 16.878460] ret_from_kernel_thread+0x14/0x1c >> [ 16.882847] >> [ 16.884351] CPU: 0 PID: 111 Comm: kunit_try_catch Tainted: G B >> 5.12.0-rc1-s3k-dev-01534-g4f14ae75edf0-dirty #4674 >> [ 16.895908] NIP: c016eb8c LR: c02f50dc CTR: c016eb38 >> [ 16.900963] REGS: e2449d90 TRAP: 0301 Tainted: G B >> (5.12.0-rc1-s3k-dev-01534-g4f14ae75edf0-dirty) >> [ 16.911386] MSR: 00009032 <EE,ME,IR,DR,RI> CR: 22000004 XER: 00000000 >> [ 16.918153] DAR: df98800a DSISR: 20000000 >> [ 16.918153] GPR00: c02f50dc e2449e50 c1140d00 e100dd24 c084b13c 00000008 c084b32b c016eb38 >> [ 16.918153] GPR08: c0850000 df988000 c0d10000 e2449eb0 22000288 >> [ 16.936695] NIP [c016eb8c] test_invalid_access+0x54/0x108 >> [ 16.942125] LR [c02f50dc] kunit_try_run_case+0x5c/0xd0 >> [ 16.947292] Call Trace: >> [ 16.949746] [e2449e50] [c005a5ec] finish_task_switch.isra.0+0x54/0x23c (unreliable) > > The "(unreliable)" might be a clue that it's related to ppc32 stack > unwinding. Any ppc expert know what this is about? > >> [ 16.957443] [e2449eb0] [c02f50dc] kunit_try_run_case+0x5c/0xd0 >> [ 16.963319] [e2449ed0] [c02f63ec] kunit_generic_run_threadfn_adapter+0x24/0x30 >> [ 16.970574] [e2449ef0] [c004e710] kthread+0x15c/0x174 >> [ 16.975670] [e2449f30] [c001317c] ret_from_kernel_thread+0x14/0x1c >> [ 16.981896] Instruction dump: >> [ 16.984879] 8129d608 38e7eb38 81020280 911f004c 39000000 995f0024 907f0028 90ff001c >> [ 16.992710] 3949000a 915f0020 3d40c0d1 3d00c085 <8929000a> 3908adb0 812a4b98 3d40c02f >> [ 17.000711] ================================================================== >> [ 17.008223] # test_invalid_access: EXPECTATION FAILED at mm/kfence/kfence_test.c:636 >> [ 17.008223] Expected report_matches(&expect) to be true, but is false >> [ 17.023243] not ok 21 - test_invalid_access > > On a fault in test_invalid_access, KFENCE prints the stack trace based > on the information in pt_regs. So we do not think there's anything we > can do to improve stack printing pe-se. > > What's confusing is that it's only this test, and none of the others. > Given that, it might be code-gen related, which results in some subtle > issue with stack unwinding. There are a few things to try, if you feel > like it: > > -- Change the unwinder, if it's possible for ppc32. > > -- Add code to test_invalid_access(), to get the compiler to emit > different code. E.g. add a bunch (unnecessary) function calls, or add > barriers, etc. > > -- Play with compiler options. We already pass > -fno-optimize-sibling-calls for kfence_test.o to avoid tail-call > optimizations that'd hide stack trace entries. But perhaps there's > something ppc-specific we missed? > > Well, the good thing is that KFENCE detects the bad access just fine. > Since, according to the test, everything works from KFENCE's side, I'd > be happy to give my Ack: > > Acked-by: Marco Elver <elver@google.com> >
Thanks.
For you information, I've got a pile of warnings from mm/kfence/report.o . Is that expected ?
CC mm/kfence/report.o In file included from ./include/linux/printk.h:7, from ./include/linux/kernel.h:16, from mm/kfence/report.c:10: mm/kfence/report.c: In function 'kfence_report_error': ./include/linux/kern_levels.h:5:18: warning: format '%zd' expects argument of type 'signed size_t', but argument 6 has type 'ptrdiff_t' {aka 'const long int'} [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/kern_levels.h:11:18: note: in expansion of macro 'KERN_SOH' 11 | #define KERN_ERR KERN_SOH "3" /* error conditions */ | ^~~~~~~~ ./include/linux/printk.h:343:9: note: in expansion of macro 'KERN_ERR' 343 | printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) | ^~~~~~~~ mm/kfence/report.c:207:3: note: in expansion of macro 'pr_err' 207 | pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%zd):\n", | ^~~~~~ ./include/linux/kern_levels.h:5:18: warning: format '%zd' expects argument of type 'signed size_t', but argument 4 has type 'ptrdiff_t' {aka 'const long int'} [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/kern_levels.h:11:18: note: in expansion of macro 'KERN_SOH' 11 | #define KERN_ERR KERN_SOH "3" /* error conditions */ | ^~~~~~~~ ./include/linux/printk.h:343:9: note: in expansion of macro 'KERN_ERR' 343 | printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) | ^~~~~~~~ mm/kfence/report.c:216:3: note: in expansion of macro 'pr_err' 216 | pr_err("Use-after-free %s at 0x%p (in kfence-#%zd):\n", | ^~~~~~ ./include/linux/kern_levels.h:5:18: warning: format '%zd' expects argument of type 'signed size_t', but argument 2 has type 'ptrdiff_t' {aka 'const long int'} [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/kern_levels.h:24:19: note: in expansion of macro 'KERN_SOH' 24 | #define KERN_CONT KERN_SOH "c" | ^~~~~~~~ ./include/linux/printk.h:385:9: note: in expansion of macro 'KERN_CONT' 385 | printk(KERN_CONT fmt, ##__VA_ARGS__) | ^~~~~~~~~ mm/kfence/report.c:223:3: note: in expansion of macro 'pr_cont' 223 | pr_cont(" (in kfence-#%zd):\n", object_index); | ^~~~~~~ ./include/linux/kern_levels.h:5:18: warning: format '%zd' expects argument of type 'signed size_t', but argument 3 has type 'ptrdiff_t' {aka 'const long int'} [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/kern_levels.h:11:18: note: in expansion of macro 'KERN_SOH' 11 | #define KERN_ERR KERN_SOH "3" /* error conditions */ | ^~~~~~~~ ./include/linux/printk.h:343:9: note: in expansion of macro 'KERN_ERR' 343 | printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) | ^~~~~~~~ mm/kfence/report.c:233:3: note: in expansion of macro 'pr_err' 233 | pr_err("Invalid free of 0x%p (in kfence-#%zd):\n", (void *)address, | ^~~~~~
Christophe
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