Re: [PATCH v2] powerpc/kprobes: Blacklist functions running with MMU disabled on PPC32

From: Naveen N. Rao
Date: Fri Mar 27 2020 - 05:07:49 EST

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Christophe Leroy wrote:

kprobe does not handle events happening in real mode, all
functions running with MMU disabled have to be blacklisted.

As already done for PPC64, do it for PPC32.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
v2:
- Don't rename nonrecoverable as local, mark it noprobe instead.
- Add missing linux/kprobes.h include in pq2.c
---
arch/powerpc/include/asm/ppc_asm.h | 10 +++
arch/powerpc/kernel/cpu_setup_6xx.S | 4 +-
arch/powerpc/kernel/entry_32.S | 65 ++++++++------------
arch/powerpc/kernel/fpu.S | 1 +
arch/powerpc/kernel/idle_6xx.S | 2 +-
arch/powerpc/kernel/idle_e500.S | 2 +-
arch/powerpc/kernel/l2cr_6xx.S | 2 +-
arch/powerpc/kernel/misc.S | 2 +
arch/powerpc/kernel/misc_32.S | 4 +-
arch/powerpc/kernel/swsusp_32.S | 6 +-
arch/powerpc/kernel/vector.S | 1 +
arch/powerpc/mm/book3s32/hash_low.S | 38 ++++++------
arch/powerpc/mm/mem.c | 2 +
arch/powerpc/platforms/52xx/lite5200_sleep.S | 2 +
arch/powerpc/platforms/82xx/pq2.c | 3 +
arch/powerpc/platforms/83xx/suspend-asm.S | 1 +
arch/powerpc/platforms/powermac/cache.S | 2 +
arch/powerpc/platforms/powermac/sleep.S | 13 ++--
18 files changed, 86 insertions(+), 74 deletions(-)

diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
index 6b03dff61a05..e8f34ba89497 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -267,8 +267,18 @@ GLUE(.,name):
.pushsection "_kprobe_blacklist","aw"; \
PPC_LONG (entry) ; \
.popsection
+#define _NOKPROBE_ENTRY(entry) \
+ _ASM_NOKPROBE_SYMBOL(entry) \
+ _ENTRY(entry)
+#define _NOKPROBE_GLOBAL(entry) \
+ _ASM_NOKPROBE_SYMBOL(entry) \
+ _GLOBAL(entry)
#else
#define _ASM_NOKPROBE_SYMBOL(entry)
+#define _NOKPROBE_ENTRY(entry) \
+ _ENTRY(entry)
+#define _NOKPROBE_GLOBAL(entry) \
+ _GLOBAL(entry)
#endif

Michael hasn't preferred including NOKPROBE variants of those macros previously, since he would like to see some cleanups there:
https://patchwork.ozlabs.org/patch/696138/

#define FUNC_START(name) _GLOBAL(name)
diff --git a/arch/powerpc/kernel/cpu_setup_6xx.S b/arch/powerpc/kernel/cpu_setup_6xx.S
index f6517f67265a..1cb947268546 100644
--- a/arch/powerpc/kernel/cpu_setup_6xx.S
+++ b/arch/powerpc/kernel/cpu_setup_6xx.S
@@ -276,7 +276,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_NO_DPM)
* in some 750 cpus where using a not yet initialized FPU register after
* power on reset may hang the CPU
*/
-_GLOBAL(__init_fpu_registers)
+_NOKPROBE_GLOBAL(__init_fpu_registers)
mfmsr r10
ori r11,r10,MSR_FP
mtmsr r11
@@ -381,7 +381,7 @@ _GLOBAL(__save_cpu_setup)
* restore CPU state as backed up by the previous
* function. This does not include cache setting
*/
-_GLOBAL(__restore_cpu_setup)
+_NOKPROBE_GLOBAL(__restore_cpu_setup)
/* Some CR fields are volatile, we back it up all */
mfcr r7

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 16af0d8d90a8..f788d586254d 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -44,24 +44,21 @@
.align 12

#ifdef CONFIG_BOOKE
- .globl mcheck_transfer_to_handler
-mcheck_transfer_to_handler:
+_NOKPROBE_ENTRY(mcheck_transfer_to_handler)
mfspr r0,SPRN_DSRR0
stw r0,_DSRR0(r11)
mfspr r0,SPRN_DSRR1
stw r0,_DSRR1(r11)
/* fall through */

- .globl debug_transfer_to_handler
-debug_transfer_to_handler:
+_NOKPROBE_ENTRY(debug_transfer_to_handler)
mfspr r0,SPRN_CSRR0
stw r0,_CSRR0(r11)
mfspr r0,SPRN_CSRR1
stw r0,_CSRR1(r11)
/* fall through */

- .globl crit_transfer_to_handler
-crit_transfer_to_handler:
+_NOKPROBE_ENTRY(crit_transfer_to_handler)
#ifdef CONFIG_PPC_BOOK3E_MMU
mfspr r0,SPRN_MAS0
stw r0,MAS0(r11)
@@ -97,8 +94,7 @@ crit_transfer_to_handler:
#endif

#ifdef CONFIG_40x
- .globl crit_transfer_to_handler
-crit_transfer_to_handler:
+_NOKPROBE_ENTRY(crit_transfer_to_handler)
lwz r0,crit_r10@l(0)
stw r0,GPR10(r11)
lwz r0,crit_r11@l(0)
@@ -124,13 +120,11 @@ crit_transfer_to_handler:
* Note that we rely on the caller having set cr0.eq iff the exception
* occurred in kernel mode (i.e. MSR:PR = 0).
*/
- .globl transfer_to_handler_full
-transfer_to_handler_full:
+_NOKPROBE_ENTRY(transfer_to_handler_full)
SAVE_NVGPRS(r11)
/* fall through */

- .globl transfer_to_handler
-transfer_to_handler:
+_NOKPROBE_ENTRY(transfer_to_handler)
stw r2,GPR2(r11)
stw r12,_NIP(r11)
stw r9,_MSR(r11)
@@ -194,8 +188,7 @@ transfer_to_handler:
bt- 31-TLF_NAPPING,4f
bt- 31-TLF_SLEEPING,7f
#endif /* CONFIG_PPC_BOOK3S_32 || CONFIG_E500 */
- .globl transfer_to_handler_cont
-transfer_to_handler_cont:
+_NOKPROBE_ENTRY(transfer_to_handler_cont)
3:
mflr r9
tovirt_novmstack r2, r2 /* set r2 to current */
@@ -297,6 +290,7 @@ reenable_mmu:
* On kernel stack overflow, load up an initial stack pointer
* and call StackOverflow(regs), which should not return.
*/
+_ASM_NOKPROBE_SYMBOL(stack_ovf)
stack_ovf:

The current convention is to add the NOKPROBE annotation at the _end_ of the associated function/symbol...

/* sometimes we use a statically-allocated stack, which is OK. */
lis r12,_end@h
@@ -460,6 +454,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
lwz r7,_NIP(r1)
lwz r2,GPR2(r1)
lwz r1,GPR1(r1)
+syscall_exit_finish:
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
mtspr SPRN_NRI, r0
#endif
@@ -467,6 +462,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
mtspr SPRN_SRR1,r8
SYNC
RFI
+_ASM_NOKPROBE_SYMBOL(syscall_exit_finish)

... like so.

#ifdef CONFIG_44x
2: li r7,0
iccci r0,r0
@@ -750,8 +746,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPE)
addi r1,r1,INT_FRAME_SIZE
blr

- .globl fast_exception_return
-fast_exception_return:
+_NOKPROBE_ENTRY(fast_exception_return)
#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
andi. r10,r9,MSR_RI /* check for recoverable interrupt */
beq 1f /* if not, we've got problems */
@@ -780,8 +775,8 @@ fast_exception_return:

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
/* check if the exception happened in a restartable section */
-1: lis r3,exc_exit_restart_end@ha
- addi r3,r3,exc_exit_restart_end@l
+1: lis r3,.Lexc_exit_restart_end@ha
+ addi r3,r3,.Lexc_exit_restart_end@l
cmplw r12,r3
#ifdef CONFIG_PPC_BOOK3S_601
bge 2b
@@ -1005,15 +1000,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
LOAD_REG_IMMEDIATE(r10,MSR_KERNEL & ~MSR_RI)
SYNC
mtmsr r10 /* clear the RI bit */
- .globl exc_exit_restart
-exc_exit_restart:
+_NOKPROBE_ENTRY(exc_exit_restart)
lwz r12,_NIP(r1)
mtspr SPRN_SRR0,r12
mtspr SPRN_SRR1,r9
REST_4GPRS(9, r1)
lwz r1,GPR1(r1)
- .globl exc_exit_restart_end
-exc_exit_restart_end:
+.Lexc_exit_restart_end:
SYNC
RFI

@@ -1033,17 +1026,15 @@ exc_exit_restart_end:
li r10, 0
stw r10, 8(r1)
REST_2GPRS(9, r1)
- .globl exc_exit_restart
+_NOKPROBE_ENTRY(exc_exit_restart)
exc_exit_restart:
lwz r11,_NIP(r1)
lwz r12,_MSR(r1)
-exc_exit_start:
mtspr SPRN_SRR0,r11
mtspr SPRN_SRR1,r12
REST_2GPRS(11, r1)
lwz r1,GPR1(r1)
- .globl exc_exit_restart_end
-exc_exit_restart_end:
+.Lexc_exit_restart_end:

I think it would be good to break this into smaller patches to handle specific code paths, if possible. At the very least, it would be good to move changes to symbol visibility to a separate patch since this also changes the names printed in a backtrace.

- Naveen

Next message: Stephen Boyd: "[GIT PULL] clk fixes for v5.6-rc7"
Previous message: Vitaly Kuznetsov: "Re: [PATCH 2/2] KVM: LAPIC: Don't need to clear IPI delivery status for x2apic"
Next in thread: Christophe Leroy: "Re: [PATCH v2] powerpc/kprobes: Blacklist functions running with MMU disabled on PPC32"
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