On Wed, 2019-02-20 at 12:45 +0530, Akshay Adiga wrote:
> On Wed, Feb 06, 2019 at 05:28:37PM +1100, Russell Currey wrote:
> > 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: <sta...@vger.kernel.org>
> > Signed-off-by: Russell Currey <rus...@russell.cc>
> > ---
> > arch/powerpc/include/asm/cpuidle.h | 1 +
> > arch/powerpc/kernel/asm-offsets.c | 1 +
> > arch/powerpc/kernel/idle_book3s.S | 20 ++++++++++++++++++++
> > 3 files changed, 22 insertions(+)
> >
> > diff --git a/arch/powerpc/include/asm/cpuidle.h
> > b/arch/powerpc/include/asm/cpuidle.h
> > index 43e5f31fe64d..ad67dbe59498 100644
> > --- a/arch/powerpc/include/asm/cpuidle.h
> > +++ b/arch/powerpc/include/asm/cpuidle.h
> > @@ -77,6 +77,7 @@ struct stop_sprs {
> > u64 mmcr1;
> > u64 mmcr2;
> > u64 mmcra;
> > + u64 iamr;
> > };
> >
> > #define PNV_IDLE_NAME_LEN 16
> > diff --git a/arch/powerpc/kernel/asm-offsets.c
> > b/arch/powerpc/kernel/asm-offsets.c
> > index 9ffc72ded73a..10e0314c2b0d 100644
> > --- a/arch/powerpc/kernel/asm-offsets.c
> > +++ b/arch/powerpc/kernel/asm-offsets.c
> > @@ -774,6 +774,7 @@ int main(void)
> > STOP_SPR(STOP_MMCR1, mmcr1);
> > STOP_SPR(STOP_MMCR2, mmcr2);
> > STOP_SPR(STOP_MMCRA, mmcra);
> > + STOP_SPR(STOP_IAMR, iamr);
> > #endif
> >
> > DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);
> > diff --git a/arch/powerpc/kernel/idle_book3s.S
> > b/arch/powerpc/kernel/idle_book3s.S
> > index 7f5ac2e8581b..bb4f552f6c7e 100644
> > --- a/arch/powerpc/kernel/idle_book3s.S
> > +++ b/arch/powerpc/kernel/idle_book3s.S
> > @@ -200,6 +200,12 @@ pnv_powersave_common:
> > /* Continue saving state */
> > SAVE_GPR(2, r1)
> > SAVE_NVGPRS(r1)
> > +
> > +BEGIN_FTR_SECTION
> > + mfspr r5, SPRN_IAMR
> > + std r5, STOP_IAMR(r13)
> > +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
> > +
>
> Are we trying to add for both power8 and power9 ?
> power9 would be CPU_FTR_ARCH_300.
>
If I recall correctly I had this at P9 only but for some reason I
changed it - the reason is probably just that I had it confused for
something else. Michael can you confirm this should be P9 only?
