linux-hardening - [RFC PATCH 5/6] powerpc/powernv/idle: Convert stack pointer to physical address

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Message-Id: <20221104172737.391978-6-ajd@linux.ibm.com>
Date:   Sat,  5 Nov 2022 04:27:36 +1100
From:   Andrew Donnellan <ajd@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     ruscur@...sell.cc, cmr@...escreens.de,
        linux-hardening@...r.kernel.org, christophe.leroy@...roup.eu
Subject: [RFC PATCH 5/6] powerpc/powernv/idle: Convert stack pointer to physical address

When we go into idle, we must disable the MMU. Currently, we can still
access the stack once the MMU is disabled, because the stack is in the
linear map.

Once we enable CONFIG_VMAP_STACK, the normal stack pointer will be in the
vmalloc area. To cope with this, manually convert the stack pointer to a
physical address using stack_pa() before going into idle, and restore the
original pointer on the way back out.

Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>

---

This currently doesn't boot on my POWER9. I'm also going to clean this up
to use the helpers from earlier in this series.
---
 arch/powerpc/platforms/powernv/idle.c | 47 +++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 841cb7f31f4f..6430fb488981 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -22,6 +22,7 @@
 #include <asm/smp.h>
 #include <asm/runlatch.h>
 #include <asm/dbell.h>
+#include <asm/reg.h>
 
 #include "powernv.h"
 #include "subcore.h"
@@ -509,6 +510,11 @@ static unsigned long power7_offline(void)
 {
 	unsigned long srr1;
 
+#ifdef CONFIG_VMAP_STACK
+	unsigned long ksp_ea = current_stack_pointer;
+	current_stack_pointer = (unsigned long)stack_pa((void *)ksp_ea);
+#endif
+
 	mtmsr(MSR_IDLE);
 
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
@@ -543,6 +549,9 @@ static unsigned long power7_offline(void)
 		srr1 = idle_kvm_start_guest(srr1);
 #endif
 
+#ifdef CONFIG_VMAP_STACK
+	current_stack_pointer = ksp_ea;
+#endif
 	mtmsr(MSR_KERNEL);
 
 	return srr1;
@@ -552,14 +561,24 @@ static unsigned long power7_offline(void)
 void power7_idle_type(unsigned long type)
 {
 	unsigned long srr1;
+#ifdef CONFIG_VMAP_STACK
+	unsigned long ksp_ea;
+#endif
 
 	if (!prep_irq_for_idle_irqsoff())
 		return;
 
+#ifdef CONFIG_VMAP_STACK
+	ksp_ea = current_stack_pointer;
+	current_stack_pointer = (unsigned long)stack_pa((void *)ksp_ea);
+#endif
 	mtmsr(MSR_IDLE);
 	__ppc64_runlatch_off();
 	srr1 = power7_idle_insn(type);
 	__ppc64_runlatch_on();
+#ifdef CONFIG_VMAP_STACK
+	current_stack_pointer = ksp_ea;
+#endif
 	mtmsr(MSR_KERNEL);
 
 	fini_irq_for_idle_irqsoff();
@@ -615,6 +634,9 @@ static unsigned long power9_idle_stop(unsigned long psscr)
 	unsigned long mmcra = 0;
 	struct p9_sprs sprs = {}; /* avoid false used-uninitialised */
 	bool sprs_saved = false;
+#ifdef CONFIG_VMAP_STACK
+	unsigned long ksp_ea;
+#endif
 
 	if (!(psscr & (PSSCR_EC|PSSCR_ESL))) {
 		/* EC=ESL=0 case */
@@ -633,7 +655,7 @@ static unsigned long power9_idle_stop(unsigned long psscr)
 		 */
 		BUG_ON((srr1 & SRR1_WAKESTATE) != SRR1_WS_NOLOSS);
 
-		goto out;
+		goto out_noloss;
 	}
 
 	/* EC=ESL=1 case */
@@ -688,6 +710,10 @@ static unsigned long power9_idle_stop(unsigned long psscr)
 	sprs.iamr	= mfspr(SPRN_IAMR);
 	sprs.uamor	= mfspr(SPRN_UAMOR);
 
+#ifdef CONFIG_VMAP_STACK
+	ksp_ea = current_stack_pointer;
+	current_stack_pointer = (unsigned long)stack_pa((void *)ksp_ea);
+#endif
 	srr1 = isa300_idle_stop_mayloss(psscr);		/* go idle */
 
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
@@ -797,6 +823,10 @@ static unsigned long power9_idle_stop(unsigned long psscr)
 		__slb_restore_bolted_realmode();
 
 out:
+#ifdef CONFIG_VMAP_STACK
+	current_stack_pointer = ksp_ea;
+#endif
+out_noloss:
 	mtmsr(MSR_KERNEL);
 
 	return srr1;
@@ -898,6 +928,9 @@ static unsigned long power10_idle_stop(unsigned long psscr)
 	unsigned long pls;
 //	struct p10_sprs sprs = {}; /* avoid false used-uninitialised */
 	bool sprs_saved = false;
+#ifdef CONFIG_VMAP_STACK
+	unsigned long ksp_ea;
+#endif
 
 	if (!(psscr & (PSSCR_EC|PSSCR_ESL))) {
 		/* EC=ESL=0 case */
@@ -916,7 +949,7 @@ static unsigned long power10_idle_stop(unsigned long psscr)
 		 */
 		BUG_ON((srr1 & SRR1_WAKESTATE) != SRR1_WS_NOLOSS);
 
-		goto out;
+		goto out_noloss;
 	}
 
 	/* EC=ESL=1 case */
@@ -927,7 +960,11 @@ static unsigned long power10_idle_stop(unsigned long psscr)
 
 		atomic_start_thread_idle();
 	}
-
+#ifdef CONFIG_VMAP_STACK
+	ksp_ea = current_stack_pointer;
+	current_stack_pointer = (unsigned long)stack_pa((void *)ksp_ea);
+#endif /* CONFIG_VMAP_STACK */
+	mtmsr(MSR_IDLE);
 	srr1 = isa300_idle_stop_mayloss(psscr);		/* go idle */
 
 	psscr = mfspr(SPRN_PSSCR);
@@ -982,6 +1019,10 @@ static unsigned long power10_idle_stop(unsigned long psscr)
 		__slb_restore_bolted_realmode();
 
 out:
+#ifdef CONFIG_VMAP_STACK
+	current_stack_pointer = ksp_ea;
+#endif /* CONFIG_VMAP_STACK */
+out_noloss:
 	mtmsr(MSR_KERNEL);
 
 	return srr1;
-- 
2.38.1