[RFC PATCH v1 12/41] powerpc/32: Remove ksp_limit

From: Christophe Leroy
Date: Tue Feb 09 2021 - 05:07:28 EST

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ksp_limit is there to help detect stack overflows.
That is specific to ppc32 as it was removed from ppc64 in
commit cbc9565ee826 ("powerpc: Remove ksp_limit on ppc64").

There are other means for detecting stack overflows.

As ppc64 has proven to not need it, ppc32 should be able to do
without it too.

Lets remove it and simplify exception handling.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/include/asm/processor.h | 2 -
arch/powerpc/kernel/asm-offsets.c | 2 -
arch/powerpc/kernel/entry_32.S | 63 ----------------------------
arch/powerpc/kernel/head_40x.S | 2 -
arch/powerpc/kernel/head_booke.h | 1 -
arch/powerpc/kernel/misc_32.S | 14 -------
arch/powerpc/kernel/process.c | 3 --
arch/powerpc/kernel/traps.c | 9 ----
arch/powerpc/lib/sstep.c | 9 ----
9 files changed, 105 deletions(-)

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 8acc3590c971..43cbd9281055 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -144,7 +144,6 @@ struct thread_struct {
#endif
#ifdef CONFIG_PPC32
void *pgdir; /* root of page-table tree */
- unsigned long ksp_limit; /* if ksp <= ksp_limit stack overflow */
#ifdef CONFIG_PPC_RTAS
unsigned long rtas_sp; /* stack pointer for when in RTAS */
#endif
@@ -282,7 +281,6 @@ struct thread_struct {
#ifdef CONFIG_PPC32
#define INIT_THREAD { \
.ksp = INIT_SP, \
- .ksp_limit = INIT_SP_LIMIT, \
.pgdir = swapper_pg_dir, \
.fpexc_mode = MSR_FE0 | MSR_FE1, \
SPEFSCR_INIT \
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index b12d7c049bfe..1f47d4e0f3b5 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -91,7 +91,6 @@ int main(void)
DEFINE(SIGSEGV, SIGSEGV);
DEFINE(NMI_MASK, NMI_MASK);
#else
- OFFSET(KSP_LIMIT, thread_struct, ksp_limit);
#ifdef CONFIG_PPC_RTAS
OFFSET(RTAS_SP, thread_struct, rtas_sp);
#endif
@@ -382,7 +381,6 @@ int main(void)
DEFINE(_CSRR1, STACK_INT_FRAME_SIZE+offsetof(struct exception_regs, csrr1));
DEFINE(_DSRR0, STACK_INT_FRAME_SIZE+offsetof(struct exception_regs, dsrr0));
DEFINE(_DSRR1, STACK_INT_FRAME_SIZE+offsetof(struct exception_regs, dsrr1));
- DEFINE(SAVED_KSP_LIMIT, STACK_INT_FRAME_SIZE+offsetof(struct exception_regs, saved_ksp_limit));
#endif
#endif

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 971980d71b04..23f46e697546 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -94,12 +94,6 @@ crit_transfer_to_handler:
mfspr r0,SPRN_SRR1
stw r0,_SRR1(r11)

- /* set the stack limit to the current stack */
- mfspr r8,SPRN_SPRG_THREAD
- lwz r0,KSP_LIMIT(r8)
- stw r0,SAVED_KSP_LIMIT(r11)
- rlwinm r0,r1,0,0,(31 - THREAD_SHIFT)
- stw r0,KSP_LIMIT(r8)
/* fall through */
_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
#endif
@@ -107,12 +101,6 @@ _ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
#ifdef CONFIG_40x
.globl crit_transfer_to_handler
crit_transfer_to_handler:
- /* set the stack limit to the current stack */
- mfspr r8,SPRN_SPRG_THREAD
- lwz r0,KSP_LIMIT(r8)
- stw r0,saved_ksp_limit@l(0)
- rlwinm r0,r1,0,0,(31 - THREAD_SHIFT)
- stw r0,KSP_LIMIT(r8)
/* fall through */
_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
#endif
@@ -156,12 +144,6 @@ transfer_to_handler:
*/
kuap_save_and_lock r11, r12, r9, r2, r6
addi r2, r12, -THREAD
-#ifndef CONFIG_VMAP_STACK
- lwz r9,KSP_LIMIT(r12)
- cmplw r1,r9 /* if r1 <= ksp_limit */
- ble- stack_ovf /* then the kernel stack overflowed */
-#endif
-5:
#if defined(CONFIG_PPC_BOOK3S_32) || defined(CONFIG_E500)
lwz r12,TI_LOCAL_FLAGS(r2)
mtcrf 0x01,r12
@@ -204,37 +186,6 @@ transfer_to_handler_cont:
_ASM_NOKPROBE_SYMBOL(transfer_to_handler)
_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont)

-#ifndef CONFIG_VMAP_STACK
-/*
- * On kernel stack overflow, load up an initial stack pointer
- * and call StackOverflow(regs), which should not return.
- */
-stack_ovf:
- /* sometimes we use a statically-allocated stack, which is OK. */
- lis r12,_end@h
- ori r12,r12,_end@l
- cmplw r1,r12
- ble 5b /* r1 <= &_end is OK */
- SAVE_NVGPRS(r11)
- addi r3,r1,STACK_FRAME_OVERHEAD
- lis r1,init_thread_union@ha
- addi r1,r1,init_thread_union@l
- addi r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
- lis r9,StackOverflow@ha
- addi r9,r9,StackOverflow@l
- LOAD_REG_IMMEDIATE(r10,MSR_KERNEL)
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
- mtspr SPRN_NRI, r0
-#endif
- mtspr SPRN_SRR0,r9
- mtspr SPRN_SRR1,r10
- rfi
-#ifdef CONFIG_40x
- b . /* Prevent prefetch past rfi */
-#endif
-_ASM_NOKPROBE_SYMBOL(stack_ovf)
-#endif
-
.globl transfer_to_syscall
transfer_to_syscall:
SAVE_NVGPRS(r1)
@@ -814,11 +765,6 @@ _ASM_NOKPROBE_SYMBOL(exc_exit_restart)
#ifdef CONFIG_40x
.globl ret_from_crit_exc
ret_from_crit_exc:
- mfspr r9,SPRN_SPRG_THREAD
- lis r10,saved_ksp_limit@ha;
- lwz r10,saved_ksp_limit@l(r10);
- tovirt(r9,r9);
- stw r10,KSP_LIMIT(r9)
lis r9,crit_srr0@ha;
lwz r9,crit_srr0@l(r9);
lis r10,crit_srr1@ha;
@@ -832,9 +778,6 @@ _ASM_NOKPROBE_SYMBOL(ret_from_crit_exc)
#ifdef CONFIG_BOOKE
.globl ret_from_crit_exc
ret_from_crit_exc:
- mfspr r9,SPRN_SPRG_THREAD
- lwz r10,SAVED_KSP_LIMIT(r1)
- stw r10,KSP_LIMIT(r9)
RESTORE_xSRR(SRR0,SRR1);
RESTORE_MMU_REGS;
RET_FROM_EXC_LEVEL(SPRN_CSRR0, SPRN_CSRR1, PPC_RFCI)
@@ -842,9 +785,6 @@ _ASM_NOKPROBE_SYMBOL(ret_from_crit_exc)

.globl ret_from_debug_exc
ret_from_debug_exc:
- mfspr r9,SPRN_SPRG_THREAD
- lwz r10,SAVED_KSP_LIMIT(r1)
- stw r10,KSP_LIMIT(r9)
RESTORE_xSRR(SRR0,SRR1);
RESTORE_xSRR(CSRR0,CSRR1);
RESTORE_MMU_REGS;
@@ -853,9 +793,6 @@ _ASM_NOKPROBE_SYMBOL(ret_from_debug_exc)

.globl ret_from_mcheck_exc
ret_from_mcheck_exc:
- mfspr r9,SPRN_SPRG_THREAD
- lwz r10,SAVED_KSP_LIMIT(r1)
- stw r10,KSP_LIMIT(r9)
RESTORE_xSRR(SRR0,SRR1);
RESTORE_xSRR(CSRR0,CSRR1);
RESTORE_xSRR(DSRR0,DSRR1);
diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 4bf0aee858eb..72e4962902de 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -95,8 +95,6 @@ _ENTRY(crit_dear)
.space 4
_ENTRY(crit_esr)
.space 4
-_ENTRY(saved_ksp_limit)
- .space 4

/*
* Exception prolog for critical exceptions. This is a little different
diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index 47857795f50a..4a5f0c9b652b 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h
@@ -481,7 +481,6 @@ struct exception_regs {
unsigned long csrr1;
unsigned long dsrr0;
unsigned long dsrr1;
- unsigned long saved_ksp_limit;
};

/* ensure this structure is always sized to a multiple of the stack alignment */
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index 717e658b90fd..acc410043b96 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -27,23 +27,14 @@

.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)
- stw r3, THREAD+KSP_LIMIT(r2)
stwu r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
mr r1,r3
- stw r10,8(r1)
bl __do_softirq
- lwz r10,8(r1)
lwz r1,0(r1)
lwz r0,4(r1)
- stw r10,THREAD+KSP_LIMIT(r2)
mtlr r0
blr

@@ -53,16 +44,11 @@ _GLOBAL(call_do_softirq)
_GLOBAL(call_do_irq)
mflr r0
stw r0,4(r1)
- lwz r10,THREAD+KSP_LIMIT(r2)
- stw r4, THREAD+KSP_LIMIT(r2)
stwu r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
mr r1,r4
- stw r10,8(r1)
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 e296440e9d16..384951381329 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1724,9 +1724,6 @@ 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)end_of_stack(p);
-#endif
#ifdef CONFIG_HAVE_HW_BREAKPOINT
for (i = 0; i < nr_wp_slots(); i++)
p->thread.ptrace_bps[i] = NULL;
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 39c8b7e9b91a..2afa05ad21c8 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1612,15 +1612,6 @@ DEFINE_INTERRUPT_HANDLER(alignment_exception)
bad_page_fault(regs, sig);
}

-DEFINE_INTERRUPT_HANDLER(StackOverflow)
-{
- pr_crit("Kernel stack overflow in process %s[%d], r1=%lx\n",
- current->comm, task_pid_nr(current), regs->gpr[1]);
- debugger(regs);
- show_regs(regs);
- panic("kernel stack overflow");
-}
-
DEFINE_INTERRUPT_HANDLER(stack_overflow_exception)
{
die("Kernel stack overflow", regs, SIGSEGV);
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index bb5c20d4ca91..212012f49f10 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -3086,15 +3086,6 @@ NOKPROBE_SYMBOL(analyse_instr);
*/
static nokprobe_inline int handle_stack_update(unsigned long ea, struct pt_regs *regs)
{
-#ifdef CONFIG_PPC32
- /*
- * Check if we will touch kernel stack overflow
- */
- if (ea - STACK_INT_FRAME_SIZE <= current->thread.ksp_limit) {
- printk(KERN_CRIT "Can't kprobe this since kernel stack would overflow.\n");
- return -EINVAL;
- }
-#endif /* CONFIG_PPC32 */
/*
* Check if we already set since that means we'll
* lose the previous value.
--
2.25.0

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