| Message ID | 20190208111103.4901-1-ruscur@russell.cc (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] powerpc/powernv/idle: Restore IAMR after idle | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | next/apply_patch Successfully applied |
| snowpatch_ozlabs/build-ppc64le | success | build succeeded & removed 0 sparse warning(s) |
| snowpatch_ozlabs/build-ppc64be | success | build succeeded & removed 0 sparse warning(s) |
| snowpatch_ozlabs/build-ppc64e | success | build succeeded & removed 0 sparse warning(s) |
| snowpatch_ozlabs/build-pmac32 | success | build succeeded & removed 0 sparse warning(s) |
| snowpatch_ozlabs/checkpatch | warning | total: 0 errors, 1 warnings, 0 checks, 30 lines checked |
The changes look good to me. On Fri, Feb 08, 2019 at 10:11:03PM +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: <stable@vger.kernel.org> > Signed-off-by: Russell Currey <ruscur@russell.cc> Reviewed-by: Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Russell Currey's on February 8, 2019 9:11 pm: > 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> > Signed-off-by: Russell Currey <ruscur@russell.cc> > --- > Since v1: > - no longer use paca to save IAMR, instead use _DAR (thanks mpe) > - remove isync and pnv_wakeup_noloss section (thanks Nick) Thanks for that, looks good. Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Hello Russell, On Fri, Feb 08, 2019 at 10:11:03PM +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: <stable@vger.kernel.org> > Signed-off-by: Russell Currey <ruscur@russell.cc> > --- > Since v1: > - no longer use paca to save IAMR, instead use _DAR (thanks mpe) Looks good to me. Once we move to Nick Piggin's C-based save/restore code, we will be saving all these SPR values on the stack anyway. Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> -- Thanks and Regards gautham.
diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S index 7f5ac2e8581b..551cc4649021 100644 --- a/arch/powerpc/kernel/idle_book3s.S +++ b/arch/powerpc/kernel/idle_book3s.S @@ -200,6 +200,13 @@ pnv_powersave_common: /* Continue saving state */ SAVE_GPR(2, r1) SAVE_NVGPRS(r1) + +BEGIN_FTR_SECTION + /* _DAR is unused here, so (ab)use it to save the IAMR */ + mfspr r5,SPRN_IAMR + std r5,_DAR(r1) +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) + mfcr r5 std r5,_CCR(r1) std r1,PACAR1(r13) @@ -924,6 +931,17 @@ BEGIN_FTR_SECTION END_FTR_SECTION_IFSET(CPU_FTR_HVMODE) REST_NVGPRS(r1) REST_GPR(2, r1) + +BEGIN_FTR_SECTION + /* IAMR was saved in regs->dar in pnv_powersave_common */ + ld r4,_DAR(r1) + mtspr SPRN_IAMR,r4 + /* + * 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)
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> Signed-off-by: Russell Currey <ruscur@russell.cc> --- Since v1: - no longer use paca to save IAMR, instead use _DAR (thanks mpe) - remove isync and pnv_wakeup_noloss section (thanks Nick) arch/powerpc/kernel/idle_book3s.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)