powerpc/mm: Fix CONFIG_PPC_KUAP_DEBUG on PPC32

CONFIG_PPC_KUAP_DEBUG is not selectable because it depends on PPC_32
which doesn't exists.

Fixing it leads to a deadlock due to a vital register getting
clobbered in _switch().

Change dependency to PPC32 and use r0 instead of r4 in _switch()

Fixes: e2fb9f544431 ("powerpc/32: Prepare for Kernel Userspace Access Protection")
Cc: stable@vger.kernel.org # v5.2+
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/540242f7d4573f7cdf1b3bf46bb35f743b2cd68f.1587124651.git.christophe.leroy@c-s.fr

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index a6371fb..8420abd 100644 (file)
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -732,7 +732,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPE)
        stw     r10,_CCR(r1)
        stw     r1,KSP(r3)      /* Set old stack pointer */
 
-       kuap_check r2, r4
+       kuap_check r2, r0
 #ifdef CONFIG_SMP
        /* We need a sync somewhere here to make sure that if the
         * previous task gets rescheduled on another CPU, it sees all

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 0c3c190..27a81c2 100644 (file)
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -397,7 +397,7 @@ config PPC_KUAP
 
 config PPC_KUAP_DEBUG
        bool "Extra debugging for Kernel Userspace Access Protection"
-       depends on PPC_KUAP && (PPC_RADIX_MMU || PPC_32)
+       depends on PPC_KUAP && (PPC_RADIX_MMU || PPC32)
        help
          Add extra debugging for Kernel Userspace Access Protection (KUAP)
          If you're unsure, say N.