powerpc/64: Initialise thread_info for emergency stacks
Nicholas Piggin
reviewerPATCH v2 1/1 powerpc/64: Initialise thread_info for emergency stacks
Emergency stacks have their thread_info mostly uninitialised, which in particular means garbage preempt_count values.
Emergency stack code runs with interrupts disabled entirely, and is used very rarely, so this has been unnoticed so far. It was found by a proposed new powerpc watchdog that takes a soft-NMI directly from the masked_interrupt handler and using the emergency stack. That crashed at BUG_ON(in_nmi()) in nmi_enter(). preempt_count()s were found to be garbage.
To fix this, zero the entire THREAD_SIZE allocation, and initialize the thread_info.
Reported-by Abdul Haleem <[email protected]>
Signed-off-by Nicholas Piggin <[email protected]>
--- arch/powerpc/include/asm/thread_info.h | 19 +++++++++++++++++++ arch/powerpc/kernel/setup_64.c | 13 ++++++++++--- 2 files changed, 29 insertions(+), 3 deletions(-)
arch/powerpc/include/asm/thread_info.h +19 -0
@@ -54,6 +54,7 @@ struct thread_info { .task = &tsk, \ .cpu = 0, \ .preempt_count = INIT_PREEMPT_COUNT, \ + .local_flags = 0, \ .flags = 0, \ }
@@ -62,6 +63,24 @@ struct thread_info {#define THREAD_SIZE_ORDER (THREAD_SHIFT - PAGE_SHIFT) +/* +* Emergency stacks are used for a range of things, from asynchronous +* NMIs (system reset, machine check) to synchronous, process context. +* Set HARDIRQ_OFFSET because we don't know exactly what context we +* come from or if it had a valid stack, which is about the best we +* can do. +* TODO: what to do with accounting? +*/ +#define emstack_init_thread_info (ti, c) \ +do { \ + (ti)->task = NULL; \ + (ti)->cpu = (c); \ + (ti)->preempt_count = HARDIRQ_OFFSET; \ + (ti)->local_flags = 0; \ + (ti)->flags = 0; \ + klp_init_thread_info(ti); \ +} while (0) +/* how to get the thread information struct from C */ static inline struct thread_info *current_thread_info (void ) {
arch/powerpc/kernel/setup_64.c +10 -3
@@ -633,24 +633,31 @@ void __init emergency_stack_init(void)* Since we use these as temporary stacks during secondary CPU * bringup, we need to get at them in real mode. This means they * must also be within the RMO region. +* +* The IRQ stacks allocated elsewhere in this file are zeroed and +* initialized in kernel/irq.c. These are initialized here in order +* to have emergency stacks available as early as possible. */ limit =min (safe_stack_limit (), ppc64_rma_size);for_each_possible_cpu (i) {struct thread_info *ti; ti =__va (memblock_alloc_base (THREAD_SIZE ,THREAD_SIZE , limit)); -klp_init_thread_info (ti); +memset (ti,0 ,THREAD_SIZE ); +emstack_init_thread_info (ti, i); paca[i].emergency_sp = (void *)ti +THREAD_SIZE ;#ifdef CONFIG_PPC_BOOK3S_64 /* emergency stack for NMI exception handling. */ ti =__va (memblock_alloc_base (THREAD_SIZE ,THREAD_SIZE , limit)); -klp_init_thread_info (ti); +memset (ti,0 ,THREAD_SIZE ); +emstack_init_thread_info (ti, i); paca[i].nmi_emergency_sp = (void *)ti +THREAD_SIZE ;/* emergency stack for machine check exception handling. */ ti =__va (memblock_alloc_base (THREAD_SIZE ,THREAD_SIZE , limit)); -klp_init_thread_info (ti); +memset (ti,0 ,THREAD_SIZE ); +emstack_init_thread_info (ti, i); paca[i].mc_emergency_sp = (void *)ti +THREAD_SIZE ;#endif }
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2.11.0