Re: [PATCH] powerpc/tm: Avoid possible userspace r1 corruption on reclaim
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2018-09-25 12:00:23
Michael Neuling [off-list ref] writes:
quoted hunk ↗ jump to hunk
Current we store the userspace r1 to PACATMSCRATCH before finally saving it to the thread struct. In theory an exception could be taken here (like a machine check or SLB miss) that could write PACATMSCRATCH and hence corrupt the userspace r1. The SLB fault currently doesn't touch PACATMSCRATCH, but others do. We've never actually seen this happen but it's theoretically possible. Either way, the code is fragile as it is. This patch saves r1 to the kernel stack (which can't fault) before we turn MSR[RI] back on. PACATMSCRATCH is still used but only with MSR[RI] off. We then copy r1 from the kernel stack to the thread struct once we have MSR[RI] back on. Suggested-by: Breno Leitao <leitao@debian.org> Signed-off-by: Michael Neuling <redacted> --- arch/powerpc/kernel/tm.S | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/kernel/tm.S b/arch/powerpc/kernel/tm.S index 701b0f5b09..8207816a1e 100644 --- a/arch/powerpc/kernel/tm.S +++ b/arch/powerpc/kernel/tm.S@@ -178,6 +178,12 @@ _GLOBAL(tm_reclaim) std r11, GPR11(r1) /* Temporary stash */ + /* Move r1 to kernel stack in case PACATMSCRATCH is used once + * we turn on RI + */
I see we still need to send you to Comment Formatting Re-Education Camp. I rewrote it a bit too, to hopefully be clearer? /* * Move the saved user r1 to the kernel stack in case PACATMSCRATCH is * clobbered by an exception once we turn on MSR_RI below. */ ld r11, PACATMSCRATCH(r13) std r11, GPR1(r1) cheers