From 71b20cdb4353274ce071fde797e5ed428e5ac54a Mon Sep 17 00:00:00 2001 From: Russell Currey Date: Thu, 18 Apr 2019 16:51:16 +1000 Subject: [PATCH] powerpc/powernv/idle: Restore IAMR after idle commit a3f3072db6cad40895c585dce65e36aab997f042 upstream. Without restoring the IAMR after idle, execution prevention on POWER9 with Radix MMU is overwritten and the kernel can freely execute userspace without faulting. This is necessary when returning from any stop state that modifies user state, as well as hypervisor state. To test how this fails without this patch, load the lkdtm driver and do the following: $ echo EXEC_USERSPACE > /sys/kernel/debug/provoke-crash/DIRECT which won't fault, then boot the kernel with powersave=off, where it will fault. Applying this patch will fix this. Fixes: 3b10d0095a1e ("powerpc/mm/radix: Prevent kernel execution of user space") Cc: stable@vger.kernel.org # v4.10+ Signed-off-by: Russell Currey Reviewed-by: Akshay Adiga Reviewed-by: Nicholas Piggin Signed-off-by: Michael Ellerman Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kernel/idle_book3s.S | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S index 7f5ac2e8581b..36178000a2f2 100644 --- a/arch/powerpc/kernel/idle_book3s.S +++ b/arch/powerpc/kernel/idle_book3s.S @@ -170,6 +170,9 @@ core_idle_lock_held: bne- core_idle_lock_held blr +/* Reuse an unused pt_regs slot for IAMR */ +#define PNV_POWERSAVE_IAMR _DAR + /* * Pass requested state in r3: * r3 - PNV_THREAD_NAP/SLEEP/WINKLE in POWER8 @@ -200,6 +203,12 @@ pnv_powersave_common: /* Continue saving state */ SAVE_GPR(2, r1) SAVE_NVGPRS(r1) + +BEGIN_FTR_SECTION + mfspr r5, SPRN_IAMR + std r5, PNV_POWERSAVE_IAMR(r1) +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) + mfcr r5 std r5,_CCR(r1) std r1,PACAR1(r13) @@ -924,6 +933,17 @@ BEGIN_FTR_SECTION END_FTR_SECTION_IFSET(CPU_FTR_HVMODE) REST_NVGPRS(r1) REST_GPR(2, r1) + +BEGIN_FTR_SECTION + /* IAMR was saved in pnv_powersave_common() */ + ld r5, PNV_POWERSAVE_IAMR(r1) + mtspr SPRN_IAMR, r5 + /* + * We don't need an isync here because the upcoming mtmsrd is + * execution synchronizing. + */ +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) + ld r4,PACAKMSR(r13) ld r5,_LINK(r1) ld r6,_CCR(r1) -- GitLab