From: Russell Currey ruscur@russell.cc
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 ruscur@russell.cc Reviewed-by: Akshay Adiga akshay.adiga@linux.vnet.ibm.com Reviewed-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/idle_book3s.S | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
--- 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)