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[80.7.220.175]) by smtp.gmail.com with ESMTPSA id h2sm340446wmb.12.2022.01.12.09.29.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Jan 2022 09:29:05 -0800 (PST) Date: Wed, 12 Jan 2022 17:29:03 +0000 From: Daniel Thompson To: Arnd Bergmann Cc: Russell King , Arnd Bergmann , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Linus Walleij Subject: Re: [PATCH v5 08/10] ARM: uaccess: add __{get,put}_kernel_nofault Message-ID: References: <20210726141141.2839385-1-arnd@kernel.org> <20210726141141.2839385-9-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210726141141.2839385-9-arnd@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 26, 2021 at 04:11:39PM +0200, Arnd Bergmann wrote: > From: Arnd Bergmann > > These mimic the behavior of get_user and put_user, except > for domain switching, address limit checking and handling > of mismatched sizes, none of which are relevant here. > > To work with pre-Armv6 kernels, this has to avoid TUSER() > inside of the new macros, the new approach passes the "t" > string along with the opcode, which is a bit uglier but > avoids duplicating more code. > > As there is no __get_user_asm_dword(), I work around it > by copying 32 bit at a time, which is possible because > the output size is known. > > Signed-off-by: Arnd Bergmann I've just been bisecting some regressions running the kgdbts tests on arm and this patch came up. It looks like once this patch applies then copy_from_kernel_nofault() starts faulting when it called from kgdb. I've put an example stack trace at the bottom of this mail and the most simplified reproduction I currently have is: ~~~ make multi_v7_defconfig ../scripts/config --enable KGDB --enable KGDB_TESTS make olddefconfig make -j `nproc` qemu-system-arm -M virt -m 1G -nographic \ -kernel arch/arm/boot/zImage -initrd rootfs.cpio.gz # Boot and login echo V1 > /sys/module/kgdbts/parameters/kgdbts ~~~ I suspect this will reproduce on any arm system with CONFIG_KGDB and CONFIG_KGDB_TESTS enabled simply by running that last echo command... but I have only tested on QEMU for now. Daniel. Stack trace: ~~~ # echo kgdbts=V1F1000 > /sys/module/kgdbts/parameters/kgdbts [ 34.995507] KGDB: Registered I/O driver kgdbts [ 35.038102] kgdbts:RUN plant and detach test Entering kdb (current=0xd4264380, pid 134) on processor 0 due to Keyboard Entry [0]kdb> [ 35.056005] kgdbts:RUN sw breakpoint test [ 35.062309] kgdbts:RUN bad memory access test [ 35.063619] 8<--- cut here --- [ 35.064022] Unhandled fault: page domain fault (0x01b) at 0x00000000 [ 35.064212] pgd = (ptrval) [ 35.064459] [00000000] *pgd=942dc835, *pte=00000000, *ppte=00000000 [ 35.065071] Internal error: : 1b [#1] SMP ARM [ 35.065381] KGDB: re-enter exception: ALL breakpoints killed [ 35.065850] ---[ end trace 909d8c43057666be ]--- [ 35.066088] 8<--- cut here --- [ 35.066189] Unhandled fault: page domain fault (0x01b) at 0x00000000 [ 35.066332] pgd = (ptrval) [ 35.066406] [00000000] *pgd=942dc835, *pte=00000000, *ppte=00000000 [ 35.066597] Internal error: : 1b [#2] SMP ARM [ 35.066906] CPU: 0 PID: 134 Comm: sh Tainted: G D 5.14.0-rc1-00013-g2df4c9a741a0 #60 [ 35.067152] Hardware name: ARM-Versatile Express [ 35.067432] [] (unwind_backtrace) from [] (show_stack+0x10/0x14) [ 35.067880] [] (show_stack) from [] (dump_stack_lvl+0x58/0x70) [ 35.068054] [] (dump_stack_lvl) from [] (kgdb_reenter_check+0x104/0x150) [ 35.068213] [] (kgdb_reenter_check) from [] (kgdb_handle_exception+0xa4/0x114) [ 35.068395] [] (kgdb_handle_exception) from [] (kgdb_notify+0x30/0x74) [ 35.068563] [] (kgdb_notify) from [] (atomic_notifier_call_chain+0xac/0x194) [ 35.068745] [] (atomic_notifier_call_chain) from [] (notify_die+0x5c/0xbc) [ 35.068933] [] (notify_die) from [] (die+0x140/0x544) [ 35.069079] [] (die) from [] (do_DataAbort+0xb8/0xbc) [ 35.069220] [] (do_DataAbort) from [] (__dabt_svc+0x5c/0xa0) [ 35.069434] Exception stack(0xd4249c10 to 0xd4249c58) [ 35.069616] 9c00: ???????? ???????? ???????? ???????? [ 35.069776] 9c20: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ???????? [ 35.069943] 9c40: ???????? ???????? ???????? ???????? ???????? ???????? [ 35.070107] [] (__dabt_svc) from [] (copy_from_kernel_nofault+0x114/0x13c) [ 35.070291] [] (copy_from_kernel_nofault) from [] (kgdb_mem2hex+0x1c/0x88) [ 35.070463] [] (kgdb_mem2hex) from [] (gdb_serial_stub+0x8c4/0x1088) [ 35.070640] [] (gdb_serial_stub) from [] (kgdb_cpu_enter+0x4f4/0x988) [ 35.070796] [] (kgdb_cpu_enter) from [] (kgdb_handle_exception+0xe0/0x114) [ 35.070982] [] (kgdb_handle_exception) from [] (kgdb_compiled_brk_fn+0x24/0x2c) [ 35.071166] [] (kgdb_compiled_brk_fn) from [] (do_undefinstr+0x104/0x230) [ 35.071342] [] (do_undefinstr) from [] (__und_svc_finish+0x0/0x54) [ 35.071502] Exception stack(0xd4249dc8 to 0xd4249e10) [ 35.071614] 9dc0: ???????? ???????? ???????? ???????? ???????? ???????? [ 35.071778] 9de0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ???????? [ 35.071944] 9e00: ???????? ???????? ???????? ???????? [ 35.072054] [] (__und_svc_finish) from [] (kgdb_breakpoint+0x30/0x58) [ 35.072211] [] (kgdb_breakpoint) from [] (configure_kgdbts+0x228/0x68c) [ 35.072395] [] (configure_kgdbts) from [] (param_attr_store+0x60/0xb8) [ 35.072560] [] (param_attr_store) from [] (kernfs_fop_write_iter+0x110/0x1d4) [ 35.072745] [] (kernfs_fop_write_iter) from [] (vfs_write+0x350/0x508) [ 35.072920] [] (vfs_write) from [] (ksys_write+0x64/0xdc) [ 35.073075] [] (ksys_write) from [] (ret_fast_syscall+0x0/0x2c) [ 35.073259] Exception stack(0xd4249fa8 to 0xd4249ff0) [ 35.073372] 9fa0: ???????? ???????? ???????? ???????? ???????? ???????? [ 35.073527] 9fc0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ???????? [ 35.073679] 9fe0: ???????? ???????? ???????? ???????? [ 35.073960] Kernel panic - not syncing: Recursive entry to debugger [ 36.286118] SMP: failed to stop secondary CPUs [ 36.286568] ---[ end Kernel panic - not syncing: Recursive entry to debugger ]--- ~~~