Since commit b86fb88855ea ("powerpc/32: implement fast entry for
syscalls on non BOOKE") and commit 1a4b739bbb4f ("powerpc/32:
implement fast entry for syscalls on BOOKE"), syscalls from
kernel are unexpected and can have catastrophic consequences
as it will destroy the kernel stack.
Test MSR_PR on syscall entry. In case syscall is from kernel,
emit a warning and return ENOSYS error.
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
v2: Rebased on powerpc/next-test, ie on top of VMAP_STACK series
v3:
- Rebased on today's powerpc/merge.
- Reloading both SRR0 and SRR1 in ret_from_kernel_syscall allthough
SRR1 is already in r9 at the time being, allows more flexibility and
less prone to risk of errors for future changes in the syscall entry.
Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
arch/powerpc/kernel/entry_32.S | 27 +++++++++++++++++++++++++++
arch/powerpc/kernel/head_32.h | 16 +++++++++-------
arch/powerpc/kernel/head_booke.h | 5 ++++-
3 files changed, 40 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 77abbc34bbe0..e808626ff230 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -575,6 +575,33 @@ syscall_exit_work:
bl do_syscall_trace_leave
b ret_from_except_full
+ /*
+ * System call was called from kernel. We get here with SRR1 in r9.
+ * Mark the exception as recoverable once we have retrieved SRR0,
+ * trap a warning and return ENOSYS with CR[SO] set.
+ */
+ .globl ret_from_kernel_syscall
+ret_from_kernel_syscall:
+ mfspr r9, SPRN_SRR0
+ mfspr r10, SPRN_SRR1
+#if !defined(CONFIG_4xx) && !defined(CONFIG_BOOKE)
+ LOAD_REG_IMMEDIATE(r11, MSR_KERNEL & ~(MSR_IR|MSR_DR))
+ mtmsr r11
+#endif
+
+0: trap
+ EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
+
+ li r3, ENOSYS
+ crset so
+#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
+ mtspr SPRN_NRI, r0
+#endif
+ mtspr SPRN_SRR0, r9
+ mtspr SPRN_SRR1, r10
+ SYNC
+ RFI
+
/*
* The fork/clone functions need to copy the full register set into
* the child process. Therefore we need to save all the nonvolatile
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index a6a5fbbf8504..0e7bf28fe53a 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -111,14 +111,16 @@
.macro SYSCALL_ENTRY trapno
mfspr r12,SPRN_SPRG_THREAD
+ mfspr r9, SPRN_SRR1
#ifdef CONFIG_VMAP_STACK
- mfspr r9, SPRN_SRR0
- mfspr r11, SPRN_SRR1
- stw r9, SRR0(r12)
- stw r11, SRR1(r12)
+ mfspr r11, SPRN_SRR0
+ stw r11, SRR0(r12)
+ stw r9, SRR1(r12)
#endif
mfcr r10
+ andi. r11, r9, MSR_PR
lwz r11,TASK_STACK-THREAD(r12)
+ beq- 99f
rlwinm r10,r10,0,4,2 /* Clear SO bit in CR */
addi r11, r11, THREAD_SIZE - INT_FRAME_SIZE
#ifdef CONFIG_VMAP_STACK
@@ -128,15 +130,14 @@
#endif
tovirt_vmstack r12, r12
tophys_novmstack r11, r11
- mflr r9
stw r10,_CCR(r11) /* save registers */
- stw r9, _LINK(r11)
+ mflr r10
+ stw r10, _LINK(r11)
#ifdef CONFIG_VMAP_STACK
lwz r10, SRR0(r12)
lwz r9, SRR1(r12)
#else
mfspr r10,SPRN_SRR0
- mfspr r9,SPRN_SRR1
#endif
stw r1,GPR1(r11)
stw r1,0(r11)
@@ -209,6 +210,7 @@
mtspr SPRN_SRR0,r11
SYNC
RFI /* jump to handler, enable MMU */
+99: b ret_from_kernel_syscall
.endm
.macro save_dar_dsisr_on_stack reg1, reg2, sp
diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index 37fc84ed90e3..bd2e5ed8dd50 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h
@@ -104,16 +104,18 @@ FTR_SECTION_ELSE
#ifdef CONFIG_KVM_BOOKE_HV
ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
#endif
+ mfspr r9, SPRN_SRR1
BOOKE_CLEAR_BTB(r11)
+ andi. r11, r9, MSR_PR
lwz r11, TASK_STACK - THREAD(r10)
rlwinm r12,r12,0,4,2 /* Clear SO bit in CR */
+ beq- 99f
ALLOC_STACK_FRAME(r11, THREAD_SIZE - INT_FRAME_SIZE)
stw r12, _CCR(r11) /* save various registers */
mflr r12
stw r12,_LINK(r11)
mfspr r12,SPRN_SRR0
stw r1, GPR1(r11)
- mfspr r9,SPRN_SRR1
stw r1, 0(r11)
mr r1, r11
stw r12,_NIP(r11)
@@ -176,6 +178,7 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
mtspr SPRN_SRR0,r11
SYNC
RFI /* jump to handler, enable MMU */
+99: b ret_from_kernel_syscall
.endm
/* To handle the additional exception priority levels on 40x and Book-E
--
2.25.0
