This is a note to let you know that I've just added the patch titled RISC-V: Fixup get incorrect user mode PC for kernel mode regs to the 5.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: risc-v-fixup-get-incorrect-user-mode-pc-for-kernel-mode-regs.patch and it can be found in the queue-5.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 59c026c359c30f116fef6ee958e24d04983efbb0 Mon Sep 17 00:00:00 2001 From: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx> Date: Thu, 11 Aug 2022 15:41:46 +0800 Subject: RISC-V: Fixup get incorrect user mode PC for kernel mode regs From: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx> commit 59c026c359c30f116fef6ee958e24d04983efbb0 upstream. When use 'echo c > /proc/sysrq-trigger' to trigger kdump, riscv_crash_save_regs() will be called to save regs for vmcore, we found "epc" value 00ffffffa5537400 is not a valid kernel virtual address, but is a user virtual address. Other regs(eg, ra, sp, gp...) are correct kernel virtual address. Actually 0x00ffffffb0dd9400 is the user mode PC of 'PID: 113 Comm: sh', which is saved in the task's stack. [ 21.201701] CPU: 0 PID: 113 Comm: sh Kdump: loaded Not tainted 5.18.9 #45 [ 21.201979] Hardware name: riscv-virtio,qemu (DT) [ 21.202160] epc : 00ffffffa5537400 ra : ffffffff80088640 sp : ff20000010333b90 [ 21.202435] gp : ffffffff810dde38 tp : ff6000000226c200 t0 : ffffffff8032be7c [ 21.202707] t1 : 0720072007200720 t2 : 30203a7375746174 s0 : ff20000010333cf0 [ 21.202973] s1 : 0000000000000000 a0 : ff20000010333b98 a1 : 0000000000000001 [ 21.203243] a2 : 0000000000000010 a3 : 0000000000000000 a4 : 28c8f0aeffea4e00 [ 21.203519] a5 : 28c8f0aeffea4e00 a6 : 0000000000000009 a7 : ffffffff8035c9b8 [ 21.203794] s2 : ffffffff810df0a8 s3 : ffffffff810df718 s4 : ff20000010333b98 [ 21.204062] s5 : 0000000000000000 s6 : 0000000000000007 s7 : ffffffff80c4a468 [ 21.204331] s8 : 00ffffffef451410 s9 : 0000000000000007 s10: 00aaaaaac0510700 [ 21.204606] s11: 0000000000000001 t3 : ff60000001218f00 t4 : ff60000001218f00 [ 21.204876] t5 : ff60000001218000 t6 : ff200000103338b8 [ 21.205079] status: 0000000200000020 badaddr: 0000000000000000 cause: 0000000000000008 With the incorrect PC, the backtrace showed by crash tool as below, the first stack frame is abnormal, crash> bt PID: 113 TASK: ff60000002269600 CPU: 0 COMMAND: "sh" #0 [ff2000001039bb90] __efistub_.Ldebug_info0 at 00ffffffa5537400 <-- Abnormal #1 [ff2000001039bcf0] panic at ffffffff806578ba #2 [ff2000001039bd50] sysrq_reset_seq_param_set at ffffffff8038c030 #3 [ff2000001039bda0] __handle_sysrq at ffffffff8038c5f8 #4 [ff2000001039be00] write_sysrq_trigger at ffffffff8038cad8 #5 [ff2000001039be20] proc_reg_write at ffffffff801b7edc #6 [ff2000001039be40] vfs_write at ffffffff80152ba6 #7 [ff2000001039be80] ksys_write at ffffffff80152ece #8 [ff2000001039bed0] sys_write at ffffffff80152f46 With the patch, we can get current kernel mode PC, the output as below, [ 17.607658] CPU: 0 PID: 113 Comm: sh Kdump: loaded Not tainted 5.18.9 #42 [ 17.607937] Hardware name: riscv-virtio,qemu (DT) [ 17.608150] epc : ffffffff800078f8 ra : ffffffff8008862c sp : ff20000010333b90 [ 17.608441] gp : ffffffff810dde38 tp : ff6000000226c200 t0 : ffffffff8032be68 [ 17.608741] t1 : 0720072007200720 t2 : 666666666666663c s0 : ff20000010333cf0 [ 17.609025] s1 : 0000000000000000 a0 : ff20000010333b98 a1 : 0000000000000001 [ 17.609320] a2 : 0000000000000010 a3 : 0000000000000000 a4 : 0000000000000000 [ 17.609601] a5 : ff60000001c78000 a6 : 000000000000003c a7 : ffffffff8035c9a4 [ 17.609894] s2 : ffffffff810df0a8 s3 : ffffffff810df718 s4 : ff20000010333b98 [ 17.610186] s5 : 0000000000000000 s6 : 0000000000000007 s7 : ffffffff80c4a468 [ 17.610469] s8 : 00ffffffca281410 s9 : 0000000000000007 s10: 00aaaaaab5bb6700 [ 17.610755] s11: 0000000000000001 t3 : ff60000001218f00 t4 : ff60000001218f00 [ 17.611041] t5 : ff60000001218000 t6 : ff20000010333988 [ 17.611255] status: 0000000200000020 badaddr: 0000000000000000 cause: 0000000000000008 With the correct PC, the backtrace showed by crash tool as below, crash> bt PID: 113 TASK: ff6000000226c200 CPU: 0 COMMAND: "sh" #0 [ff20000010333b90] riscv_crash_save_regs at ffffffff800078f8 <--- Normal #1 [ff20000010333cf0] panic at ffffffff806578c6 #2 [ff20000010333d50] sysrq_reset_seq_param_set at ffffffff8038c03c #3 [ff20000010333da0] __handle_sysrq at ffffffff8038c604 #4 [ff20000010333e00] write_sysrq_trigger at ffffffff8038cae4 #5 [ff20000010333e20] proc_reg_write at ffffffff801b7ee8 #6 [ff20000010333e40] vfs_write at ffffffff80152bb2 #7 [ff20000010333e80] ksys_write at ffffffff80152eda #8 [ff20000010333ed0] sys_write at ffffffff80152f52 Fixes: e53d28180d4d ("RISC-V: Add kdump support") Co-developed-by: Guo Ren <guoren@xxxxxxxxxx> Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220811074150.3020189-3-xianting.tian@xxxxxxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/riscv/kernel/crash_save_regs.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/riscv/kernel/crash_save_regs.S +++ b/arch/riscv/kernel/crash_save_regs.S @@ -44,7 +44,7 @@ SYM_CODE_START(riscv_crash_save_regs) REG_S t6, PT_T6(a0) /* x31 */ csrr t1, CSR_STATUS - csrr t2, CSR_EPC + auipc t2, 0x0 csrr t3, CSR_TVAL csrr t4, CSR_CAUSE Patches currently in stable-queue which might be from xianting.tian@xxxxxxxxxxxxxxxxx are queue-5.18/risc-v-add-modules-to-virtual-kernel-memory-layout-dump.patch queue-5.18/risc-v-kexec-fixup-use-of-smp_processor_id-in-preemptible-context.patch queue-5.18/risc-v-fixup-schedule-out-issue-in-machine_crash_shutdown.patch queue-5.18/risc-v-fixup-get-incorrect-user-mode-pc-for-kernel-mode-regs.patch