From b74e409ea1b18128b877a50883d92a12eba83c33 Mon Sep 17 00:00:00 2001 From: Vasily Gorbik Date: Fri, 9 Apr 2021 00:13:18 +0200 Subject: [PATCH 1/2] s390/entry: avoid setting up backchain in ext|io handlers Currently when interrupt arrives to cpu while in kernel context INT_HANDLER macro (used for ext_int_handler and io_int_handler) allocates new stack frame and pt_regs on the kernel stack and sets up the backchain to jump over the pt_regs to the frame which has been interrupted. This is not ideal to two reasons: 1. This hides the fact that kernel stack contains interrupt frame in it and hence breaks arch_stack_walk_reliable(), which needs to know that to guarantee "reliability" and checks that there are no pt_regs on the way. 2. It breaks the backchain unwinder logic, which assumes that the next stack frame after an interrupt frame is reliable, while it is not. In some cases (when r14 contains garbage) this leads to early unwinding termination with an error, instead of marking frame as unreliable and continuing. To address that, only set backchain to 0. Fixes: 56e62a737028 ("s390: convert to generic entry") Reviewed-by: Sven Schnelle Signed-off-by: Vasily Gorbik Signed-off-by: Heiko Carstens --- arch/s390/kernel/entry.S | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index c10b9f31eef7..235bf2ac3359 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -401,15 +401,13 @@ ENTRY(\name) brasl %r14,.Lcleanup_sie_int #endif 0: CHECK_STACK __LC_SAVE_AREA_ASYNC - lgr %r11,%r15 aghi %r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE) - stg %r11,__SF_BACKCHAIN(%r15) j 2f 1: BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP lctlg %c1,%c1,__LC_KERNEL_ASCE lg %r15,__LC_KERNEL_STACK - xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) -2: la %r11,STACK_FRAME_OVERHEAD(%r15) +2: xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) + la %r11,STACK_FRAME_OVERHEAD(%r15) stmg %r0,%r7,__PT_R0(%r11) # clear user controlled registers to prevent speculative use xgr %r0,%r0 From a994eddb947ea9ebb7b14d9a1267001699f0a136 Mon Sep 17 00:00:00 2001 From: Vasily Gorbik Date: Fri, 9 Apr 2021 00:15:21 +0200 Subject: [PATCH 2/2] s390/entry: save the caller of psw_idle Currently psw_idle does not allocate a stack frame and does not save its r14 and r15 into the save area. Even though this is valid from call ABI point of view, because psw_idle does not make any calls explicitly, in reality psw_idle is an entry point for controlled transition into serving interrupts. So, in practice, psw_idle stack frame is analyzed during stack unwinding. Depending on build options that r14 slot in the save area of psw_idle might either contain a value saved by previous sibling call or complete garbage. [task 0000038000003c28] do_ext_irq+0xd6/0x160 [task 0000038000003c78] ext_int_handler+0xba/0xe8 [task *0000038000003dd8] psw_idle_exit+0x0/0x8 <-- pt_regs ([task 0000038000003dd8] 0x0) [task 0000038000003e10] default_idle_call+0x42/0x148 [task 0000038000003e30] do_idle+0xce/0x160 [task 0000038000003e70] cpu_startup_entry+0x36/0x40 [task 0000038000003ea0] arch_call_rest_init+0x76/0x80 So, to make a stacktrace nicer and actually point for the real caller of psw_idle in this frequently occurring case, make psw_idle save its r14. [task 0000038000003c28] do_ext_irq+0xd6/0x160 [task 0000038000003c78] ext_int_handler+0xba/0xe8 [task *0000038000003dd8] psw_idle_exit+0x0/0x6 <-- pt_regs ([task 0000038000003dd8] arch_cpu_idle+0x3c/0xd0) [task 0000038000003e10] default_idle_call+0x42/0x148 [task 0000038000003e30] do_idle+0xce/0x160 [task 0000038000003e70] cpu_startup_entry+0x36/0x40 [task 0000038000003ea0] arch_call_rest_init+0x76/0x80 Reviewed-by: Sven Schnelle Signed-off-by: Vasily Gorbik Signed-off-by: Heiko Carstens --- arch/s390/kernel/entry.S | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index 235bf2ac3359..12de7a9c85b3 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -443,6 +443,7 @@ INT_HANDLER io_int_handler,__LC_IO_OLD_PSW,do_io_irq * Load idle PSW. */ ENTRY(psw_idle) + stg %r14,(__SF_GPRS+8*8)(%r15) stg %r3,__SF_EMPTY(%r15) larl %r1,psw_idle_exit stg %r1,__SF_EMPTY+8(%r15)