powerpc/32: Warn and return ENOSYS on syscalls from kernel
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.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8ee3bdbbdfdfc64ca7001e90c43b2aee6f333578.1580470482.git.christophe.leroy@c-s.fr
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index a6a5fbb..0e7bf28 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