From cbc9565ee82694dec31d8137dec975b83175183b Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Tue, 24 Sep 2013 15:17:21 +1000 Subject: [PATCH] powerpc: Remove ksp_limit on ppc64 We've been keeping that field in thread_struct for a while, it contains the "limit" of the current stack pointer and is meant to be used for detecting stack overflows. It has a few problems however: - First, it was never actually *used* on 64-bit. Set and updated but not actually exploited - When switching stack to/from irq and softirq stacks, it's update is racy unless we hard disable interrupts, which is costly. This is fine on 32-bit as we don't soft-disable there but not on 64-bit. Thus rather than fixing 2 in order to implement 1 in some hypothetical future, let's remove the code completely from 64-bit. In order to avoid a clutter of ifdef's, we remove the updates from C code completely during interrupt stack switching, and instead maintain it from the asm helper that is used to do the stack switching in the first place. Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/processor.h | 4 +--- arch/powerpc/kernel/asm-offsets.c | 3 ++- arch/powerpc/kernel/irq.c | 12 ------------ arch/powerpc/kernel/misc_32.S | 16 ++++++++++++++++ arch/powerpc/kernel/process.c | 3 ++- arch/powerpc/lib/sstep.c | 3 ++- 6 files changed, 23 insertions(+), 18 deletions(-) diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index e378cccfca55..ce4de5aed7b5 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -149,8 +149,6 @@ typedef struct { struct thread_struct { unsigned long ksp; /* Kernel stack pointer */ - unsigned long ksp_limit; /* if ksp <= ksp_limit stack overflow */ - #ifdef CONFIG_PPC64 unsigned long ksp_vsid; #endif @@ -162,6 +160,7 @@ struct thread_struct { #endif #ifdef CONFIG_PPC32 void *pgdir; /* root of page-table tree */ + unsigned long ksp_limit; /* if ksp <= ksp_limit stack overflow */ #endif #ifdef CONFIG_PPC_ADV_DEBUG_REGS /* @@ -321,7 +320,6 @@ struct thread_struct { #else #define INIT_THREAD { \ .ksp = INIT_SP, \ - .ksp_limit = INIT_SP_LIMIT, \ .regs = (struct pt_regs *)INIT_SP - 1, /* XXX bogus, I think */ \ .fs = KERNEL_DS, \ .fpr = {{0}}, \ diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index d8958be5f31a..502c7a4e73f7 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -80,10 +80,11 @@ int main(void) DEFINE(TASKTHREADPPR, offsetof(struct task_struct, thread.ppr)); #else DEFINE(THREAD_INFO, offsetof(struct task_struct, stack)); + DEFINE(THREAD_INFO_GAP, _ALIGN_UP(sizeof(struct thread_info), 16)); + DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit)); #endif /* CONFIG_PPC64 */ DEFINE(KSP, offsetof(struct thread_struct, ksp)); - DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit)); DEFINE(PT_REGS, offsetof(struct thread_struct, regs)); #ifdef CONFIG_BOOKE DEFINE(THREAD_NORMSAVES, offsetof(struct thread_struct, normsave[0])); diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c index 2234a1276a77..57d286a78f86 100644 --- a/arch/powerpc/kernel/irq.c +++ b/arch/powerpc/kernel/irq.c @@ -496,7 +496,6 @@ void do_IRQ(struct pt_regs *regs) { struct pt_regs *old_regs = set_irq_regs(regs); struct thread_info *curtp, *irqtp; - unsigned long saved_sp_limit; /* Switch to the irq stack to handle this */ curtp = current_thread_info(); @@ -509,12 +508,6 @@ void do_IRQ(struct pt_regs *regs) return; } - /* Adjust the stack limit */ - saved_sp_limit = current->thread.ksp_limit; - current->thread.ksp_limit = (unsigned long)irqtp + - _ALIGN_UP(sizeof(struct thread_info), 16); - - /* Prepare the thread_info in the irq stack */ irqtp->task = curtp->task; irqtp->flags = 0; @@ -526,7 +519,6 @@ void do_IRQ(struct pt_regs *regs) call_do_irq(regs, irqtp); /* Restore stack limit */ - current->thread.ksp_limit = saved_sp_limit; irqtp->task = NULL; /* Copy back updates to the thread_info */ @@ -604,16 +596,12 @@ void irq_ctx_init(void) static inline void do_softirq_onstack(void) { struct thread_info *curtp, *irqtp; - unsigned long saved_sp_limit = current->thread.ksp_limit; curtp = current_thread_info(); irqtp = softirq_ctx[smp_processor_id()]; irqtp->task = curtp->task; irqtp->flags = 0; - current->thread.ksp_limit = (unsigned long)irqtp + - _ALIGN_UP(sizeof(struct thread_info), 16); call_do_softirq(irqtp); - current->thread.ksp_limit = saved_sp_limit; irqtp->task = NULL; /* Set any flag that may have been set on the diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S index 7da3882a3622..2b0ad9845363 100644 --- a/arch/powerpc/kernel/misc_32.S +++ b/arch/powerpc/kernel/misc_32.S @@ -36,25 +36,41 @@ .text +/* + * We store the saved ksp_limit in the unused part + * of the STACK_FRAME_OVERHEAD + */ _GLOBAL(call_do_softirq) mflr r0 stw r0,4(r1) + lwz r10,THREAD+KSP_LIMIT(r2) + addi r11,r3,THREAD_INFO_GAP stwu r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3) mr r1,r3 + stw r10,8(r1) + stw r11,THREAD+KSP_LIMIT(r2) bl __do_softirq + lwz r10,8(r1) lwz r1,0(r1) lwz r0,4(r1) + stw r10,THREAD+KSP_LIMIT(r2) mtlr r0 blr _GLOBAL(call_do_irq) mflr r0 stw r0,4(r1) + lwz r10,THREAD+KSP_LIMIT(r2) + addi r11,r3,THREAD_INFO_GAP stwu r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4) mr r1,r4 + stw r10,8(r1) + stw r11,THREAD+KSP_LIMIT(r2) bl __do_irq + lwz r10,8(r1) lwz r1,0(r1) lwz r0,4(r1) + stw r10,THREAD+KSP_LIMIT(r2) mtlr r0 blr diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 6f428da53e20..96d2fdf3aa9e 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1000,9 +1000,10 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, kregs = (struct pt_regs *) sp; sp -= STACK_FRAME_OVERHEAD; p->thread.ksp = sp; +#ifdef CONFIG_PPC32 p->thread.ksp_limit = (unsigned long)task_stack_page(p) + _ALIGN_UP(sizeof(struct thread_info), 16); - +#endif #ifdef CONFIG_HAVE_HW_BREAKPOINT p->thread.ptrace_bps[0] = NULL; #endif diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c index a7ee978fb860..b1faa1593c90 100644 --- a/arch/powerpc/lib/sstep.c +++ b/arch/powerpc/lib/sstep.c @@ -1505,6 +1505,7 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr) */ if ((ra == 1) && !(regs->msr & MSR_PR) \ && (val3 >= (regs->gpr[1] - STACK_INT_FRAME_SIZE))) { +#ifdef CONFIG_PPC32 /* * Check if we will touch kernel sack overflow */ @@ -1513,7 +1514,7 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr) err = -EINVAL; break; } - +#endif /* CONFIG_PPC32 */ /* * Check if we already set since that means we'll * lose the previous value.