linux-hardening - [RFC PATCH 6/6] powerpc/64s: Enable CONFIG_VMAP

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Date:   Sat,  5 Nov 2022 04:27:37 +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 6/6] powerpc/64s: Enable CONFIG_VMAP_STACK

Enable CONFIG_VMAP_STACK for book3s64.

To do this, we need to make some slight adjustments to set the stack SLB
entry up for vmalloc rather than linear.

For now, only enable if KVM_BOOK3S_64_HV is disabled (there's some real mode
handlers we need to fix there).

Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>
---
 arch/powerpc/kernel/process.c          |  4 ++++
 arch/powerpc/mm/book3s64/slb.c         | 11 +++++++++--
 arch/powerpc/platforms/Kconfig.cputype |  1 +
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 07917726c629..cadf2db5a2a8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1685,7 +1685,11 @@ static void setup_ksp_vsid(struct task_struct *p, unsigned long sp)
 {
 #ifdef CONFIG_PPC_64S_HASH_MMU
 	unsigned long sp_vsid;
+#ifdef CONFIG_VMAP_STACK
+	unsigned long llp = mmu_psize_defs[mmu_vmalloc_psize].sllp;
+#else /* CONFIG_VMAP_STACK */
 	unsigned long llp = mmu_psize_defs[mmu_linear_psize].sllp;
+#endif /* CONFIG_VMAP_STACK */
 
 	if (radix_enabled())
 		return;
diff --git a/arch/powerpc/mm/book3s64/slb.c b/arch/powerpc/mm/book3s64/slb.c
index 6956f637a38c..0e21f0eaa7bb 100644
--- a/arch/powerpc/mm/book3s64/slb.c
+++ b/arch/powerpc/mm/book3s64/slb.c
@@ -541,7 +541,7 @@ void slb_set_size(u16 size)
 void slb_initialize(void)
 {
 	unsigned long linear_llp, vmalloc_llp, io_llp;
-	unsigned long lflags;
+	unsigned long lflags, kstack_flags;
 	static int slb_encoding_inited;
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 	unsigned long vmemmap_llp;
@@ -582,11 +582,18 @@ void slb_initialize(void)
 	 * get_paca()->kstack hasn't been initialized yet.
 	 * For secondary cpus, we need to bolt the kernel stack entry now.
 	 */
+
+#ifdef CONFIG_VMAP_STACK
+	kstack_flags = SLB_VSID_KERNEL | vmalloc_llp;
+#else
+	kstack_flags = SLB_VSID_KERNEL | linear_llp;
+#endif
 	slb_shadow_clear(KSTACK_INDEX);
 	if (raw_smp_processor_id() != boot_cpuid &&
 	    (get_paca()->kstack & slb_esid_mask(mmu_kernel_ssize)) > PAGE_OFFSET)
 		create_shadowed_slbe(get_paca()->kstack,
-				     mmu_kernel_ssize, lflags, KSTACK_INDEX);
+				     mmu_kernel_ssize, kstack_flags,
+				     KSTACK_INDEX);
 
 	asm volatile("isync":::"memory");
 }
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 0c4eed9aea80..998317257797 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -104,6 +104,7 @@ config PPC_BOOK3S_64
 	select IRQ_WORK
 	select PPC_64S_HASH_MMU if !PPC_RADIX_MMU
 	select KASAN_VMALLOC if KASAN
+	select HAVE_ARCH_VMAP_STACK if KVM_BOOK3S_64_HV = n
 
 config PPC_BOOK3E_64
 	bool "Embedded processors"
-- 
2.38.1