[PATCH] powerpc: Remove ksp_limit on ppc64
Benjamin Herrenschmidt
benh at kernel.crashing.org
Tue Sep 24 15:43:13 EST 2013
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 <benh at kernel.crashing.org>
---
Applies on top of "powerpc/irq: Run softirqs off the top of the irq stack"
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 e378ccc..ce4de5a 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 d8958be..502c7a4 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 2234a12..57d286a 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 7da3882..2b0ad98 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 6f428da..96d2fdf 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 a7ee978..b1faa15 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.
More information about the Linuxppc-dev
mailing list