powerpc/32: Remove ksp_limit

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@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d789c3385b22e07bedc997613c0d26074cb513e7.1615552866.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 8acc359..43cbd92 100644 (file)
--- 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 f3a6622..7362053 100644 (file)
--- 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
@@ -381,7 +380,6 @@ 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 4ffbcf3..66198e6 100644 (file)
--- 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
@@ -151,17 +139,10 @@ transfer_to_handler:
 #endif
        b       3f
 
-2:     /* if from kernel, check interrupted DOZE/NAP mode and
-         * check for stack overflow
-         */
+       /* if from kernel, check interrupted DOZE/NAP mode */
+2:
        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 +185,6 @@ 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)
@@ -815,11 +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;
@@ -833,9 +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)
@@ -843,9 +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;
@@ -854,9 +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 4bf0aee..72e4962 100644 (file)
--- 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 4785779..4a5f0c9 100644 (file)
--- 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 717e658..acc4100 100644 (file)
--- 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 afb334d..5b30df7 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1725,9 +1725,6 @@ 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 bb13873..286b3a6 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1605,15 +1605,6 @@ bad:
                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 c6aebc1..739ea6d 100644 (file)
--- 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.