On 19/09/2023 12:39, Linu Cherian wrote: > Hi James, > >> -----Original Message----- >> From: James Clark <james.clark@xxxxxxx> >> Sent: Friday, September 15, 2023 7:20 PM >> To: Linu Cherian <lcherian@xxxxxxxxxxx>; suzuki.poulose@xxxxxxx; >> mike.leach@xxxxxxxxxx; leo.yan@xxxxxxxxxx >> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; coresight@xxxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx; >> krzysztof.kozlowski+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx; >> devicetree@xxxxxxxxxxxxxxx; Sunil Kovvuri Goutham >> <sgoutham@xxxxxxxxxxx>; George Cherian <gcherian@xxxxxxxxxxx> >> Subject: [EXT] Re: [RFC PATCH v3 0/8] Coresight for Kernel panic and >> watchdog reset >> >> External Email >> >> ---------------------------------------------------------------------- >> >> >> On 04/09/2023 06:05, Linu Cherian wrote: >>> This RFC v3 patch series is rebased on v6.5-rc7 and is dependent on >>> the below two patches. >> [...] >>> >>> Steps for reading trace data captured in previous boot >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> 1. cd /sys/bus/coresight/devices/tmc_etrXX/ >>> >>> 2. Change to special mode called, read_prevboot. >>> >>> #echo 1 > read_prevboot >>> >>> 3. Dump trace buffer data to a file, >>> >>> #dd if=/dev/tmc_etrXX of=~/cstrace.bin >> >> Hi Linu, >> >> I left this comment on V2, but I tested it again and get the same result. >> Instead of linking it I'll just re-paste it here: >> >> I made a reserved region, but when I run this command I get "Unable to >> handle kernel paging request at virtual address 001f1921ed10ffae". >> >> Is there an extra step involved if there was no trace captured from a previous >> panic? I thought I'd just be able to read out uninitialised data. Or is it the >> uninitialised metadata that's causing this issue? >> >> Also that's without KASAN or lockdep turned on. If I have a kernel with either >> of those things I get a different warning for each one. I expect the lockdep >> one would happen even in the working scenario though? > > Somehow I missed this comment on V2. > > I retried the above steps on my board and I do not see issues either with KASAN OR lockdep enabled configs. > Please see logs below. > > a. Lockdep enabled config > ~# cd /sys/bus/coresight/devices/tmc_etr0 > tmc_etr0# echo 1 > read_prevboot > tmc_etr0# dd if=/dev/tmc_etr0 of=~/cstrace.bin > 12324+1 records in > 12324+1 records out > 6310032 bytes (6.3 MB, 6.0 MiB) copied, 0.122883 s, 51.3 MB/s > > # zcat /proc/config.gz | grep LOCKDEP > CONFIG_LOCKDEP_SUPPORT=y > CONFIG_LOCKDEP=y > CONFIG_LOCKDEP_BITS=15 > CONFIG_LOCKDEP_CHAINS_BITS=16 > CONFIG_LOCKDEP_STACK_TRACE_BITS=19 > CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS=14 > CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=12 > # CONFIG_DEBUG_LOCKDEP is not set > > b. KASAN enabled config > # cd /sys/bus/coresight/devices/tmc_etr0/ > tmc_etr0# ls > buf_mode_preferred connections power trigger_cntr > buf_modes_available enable_sink read_prevboot uevent > buffer_size mgmt subsystem waiting_for_supplier > tmc_etr0# echo 1 > read_prevboot > tmc_etr0# dd if=/dev/tmc_etr0 of=~/cstrace.bin > 12324+1 records in > 12324+1 records out > 6310032 bytes (6.3 MB, 6.0 MiB) copied, 0.0940671 s, 67.1 MB/s > > ~# zcat /proc/config.gz | grep -i kasan > CONFIG_KASAN_SHADOW_OFFSET=0xdfff800000000000 > CONFIG_HAVE_ARCH_KASAN=y > CONFIG_HAVE_ARCH_KASAN_SW_TAGS=y > CONFIG_HAVE_ARCH_KASAN_HW_TAGS=y > CONFIG_HAVE_ARCH_KASAN_VMALLOC=y > CONFIG_CC_HAS_KASAN_GENERIC=y > CONFIG_CC_HAS_KASAN_SW_TAGS=y > CONFIG_KASAN=y > CONFIG_KASAN_GENERIC=y > # CONFIG_KASAN_SW_TAGS is not set > # CONFIG_KASAN_HW_TAGS is not set > CONFIG_KASAN_OUTLINE=y > # CONFIG_KASAN_INLINE is not set > CONFIG_KASAN_STACK=y > CONFIG_KASAN_VMALLOC=y > # CONFIG_KASAN_MODULE_TEST is not set > > > But then I am able to trigger kernel crash with bad metadata(corrupted rwp and rrp) with below stack trace. > > [ 107.442991] __arch_copy_to_user+0x180/0x240 > [ 107.447254] vfs_read+0xc8/0x2a8 > [ 107.450476] ksys_read+0x74/0x110 > [ 107.453783] __arm64_sys_read+0x24/0x38 > [ 107.457611] invoke_syscall.constprop.0+0x58/0xf8 > [ 107.462309] do_el0_svc+0x6c/0x158 > [ 107.465704] el0_svc+0x54/0x1c0 > [ 107.468839] el0t_64_sync_handler+0x100/0x130 > [ 107.473188] el0t_64_sync+0x190/0x198 > [ 107.476843] Code: d503201f d503201f d503201f d503201f (a8c12027) > > Does your stack trace looks similar ? Then its very likely due to bad metadata. > If not, kindly please share yours. > > For example, if we have bad values for rwp and rrp, offset can get messed up resulting in above crash. > Will add more validation checks while setting up the prevboot buffer, so as to avoid processing with bogus metadata values > in the next patch version. > > Thanks James for trying this out. > > I think it must be bad metadata because I didn't try it with a previous crash saved yet. I suppose we do need some kind of validation then if it's possible for bad metadata to cause a crash. I will try after filling in the metadata and see if that was the issue. > >> >>> >>> 4. Reset back to normal mode >>> >>> #echo 0 > read_prevboot >>>
