Re: [RFC PATCH] x86/split_lock: Disable SLD if an unaware (out-of-tree) module enables VMX

Peter Zijlstra
2020-04-06T14:04:46Z

On Mon, Apr 06, 2020 at 05:50:10AM -0700, Christoph Hellwig wrote:
> On Fri, Apr 03, 2020 at 09:30:07AM -0700, Sean Christopherson wrote:
> > Hook into native CR4 writes to disable split-lock detection if CR4.VMXE
> > is toggled on by an SDL-unaware entity, e.g. an out-of-tree hypervisor
> > module. Most/all VMX-based hypervisors blindly reflect #AC exceptions
> > into the guest, or don't intercept #AC in the first place. With SLD
> > enabled, this results in unexpected #AC faults in the guest, leading to
> > crashes in the guest and other undesirable behavior.
>
> Out of tree modules do not matter, so we should not add code just to
> work around broken third party code. If you really feel strongly just
> make sure something they rely on for their hacks stops being exported
> and they are properly broken.

Something like so then?

I couldn't find any in-tree users for unmap_kernel_range*(), and this
removes __get_vm_area() and with the ability to custom ranges. It also
removes map_vm_area() and replaces it with map_vm_area_nx() which kills
adding executable maps.

---
diff --git a/arch/powerpc/include/asm/pasemi_dma.h b/arch/powerpc/include/asm/pasemi_dma.h
index 712a0b32120f..305c54d56244 100644
--- a/arch/powerpc/include/asm/pasemi_dma.h
+++ b/arch/powerpc/include/asm/pasemi_dma.h
@@ -523,4 +523,6 @@ extern void pasemi_dma_free_fun(int fun);
/* Initialize the library, must be called before any other functions */
extern int pasemi_dma_init(void);

+extern struct vm_struct *get_phb_area(unsigned long size, unsigned long flags);
+
#endif /* ASM_PASEMI_DMA_H */
diff --git a/arch/powerpc/platforms/pasemi/dma_lib.c b/arch/powerpc/platforms/pasemi/dma_lib.c
index 270fa3c0d372..0aae02df061d 100644
--- a/arch/powerpc/platforms/pasemi/dma_lib.c
+++ b/arch/powerpc/platforms/pasemi/dma_lib.c
@@ -617,3 +617,10 @@ int pasemi_dma_init(void)
return err;
}
EXPORT_SYMBOL(pasemi_dma_init);
+
+struct vm_struct *get_phb_area(unsigned long size, unsigned long flags)
+{
+ return __get_vm_area_node(size, 1, flags, PHB_IO_BASE, PHB_IO_END, NUMA_NO_NODE,
+ GFP_KERNEL, __builtin_return_address(0));
+}
+EXPORT_SYMBOL_GPL(get_phb_area);
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 65c2ecd730c5..0bd5ea46f1d2 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -274,6 +274,11 @@ typedef struct pgprot { pgprotval_t pgprot; } pgprot_t;

typedef struct { pgdval_t pgd; } pgd_t;

+static inline pgprot_t pgprot_nx(pgprot_t prot)
+{
+ return __pgprot(pgprot_val(prot) | _PAGE_NX);
+}
+
#ifdef CONFIG_X86_PAE

/*
diff --git a/drivers/pcmcia/electra_cf.c b/drivers/pcmcia/electra_cf.c
index f2741c04289d..42eb242b29f1 100644
--- a/drivers/pcmcia/electra_cf.c
+++ b/drivers/pcmcia/electra_cf.c
@@ -22,6 +22,8 @@
#include <linux/of_platform.h>
#include <linux/slab.h>

+#include <asm/pasemi_dma.h>
+
#include <pcmcia/ss.h>

static const char driver_name[] = "electra-cf";
@@ -204,7 +206,7 @@ static int electra_cf_probe(struct platform_device *ofdev)
cf->mem_base = ioremap(cf->mem_phys, cf->mem_size);
cf->io_size = PAGE_ALIGN(resource_size(&io));

- area = __get_vm_area(cf->io_size, 0, PHB_IO_BASE, PHB_IO_END);
+ area = get_phb_area(cf->io_size, 0);
if (area == NULL) {
status = -ENOMEM;
goto fail1;
diff --git a/drivers/staging/media/ipu3/ipu3-dmamap.c b/drivers/staging/media/ipu3/ipu3-dmamap.c
index 7431322379f6..fc3fe85c340c 100644
--- a/drivers/staging/media/ipu3/ipu3-dmamap.c
+++ b/drivers/staging/media/ipu3/ipu3-dmamap.c
@@ -124,13 +124,13 @@ void *imgu_dmamap_alloc(struct imgu_device *imgu, struct imgu_css_map *map,
}

/* Now grab a virtual region */
- map->vma = __get_vm_area(size, VM_USERMAP, VMALLOC_START, VMALLOC_END);
+ map->vma = get_vm_area(size, VM_USERMAP);
if (!map->vma)
goto out_unmap;

map->vma->pages = pages;
/* And map it in KVA */
- if (map_vm_area(map->vma, PAGE_KERNEL, pages))
+ if (map_vm_area_nx(map->vma, PAGE_KERNEL, pages))
goto out_vunmap;

map->size = size;
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index e2e2bef07dd2..ee66c1f8b141 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -490,6 +490,10 @@ static inline int arch_unmap_one(struct mm_struct *mm,
#define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
#endif

+#ifndef pgprot_nx
+#define pgprot_nx(prot) (prot)
+#endif
+
#ifndef pgprot_noncached
#define pgprot_noncached(prot) (prot)
#endif
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6b8eeb0ecee5..a1c5faa6042e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2029,7 +2029,6 @@ void unmap_kernel_range_noflush(unsigned long addr, unsigned long size)
{
vunmap_page_range(addr, addr + size);
}
-EXPORT_SYMBOL_GPL(unmap_kernel_range_noflush);

/**
* unmap_kernel_range - unmap kernel VM area and flush cache and TLB
@@ -2047,7 +2046,6 @@ void unmap_kernel_range(unsigned long addr, unsigned long size)
vunmap_page_range(addr, end);
flush_tlb_kernel_range(addr, end);
}
-EXPORT_SYMBOL_GPL(unmap_kernel_range);

int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page **pages)
{
@@ -2059,7 +2057,12 @@ int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page **pages)

return err > 0 ? 0 : err;
}
-EXPORT_SYMBOL_GPL(map_vm_area);
+
+int map_vm_area_nx(struct vm_struct *area, pgprot prot, struct page **pages)
+{
+ return map_vm_area(area, pgprot_nx(prot), pages);
+}
+EXPORT_SYMBOL_GPL(map_vm_area_nx);

static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
struct vmap_area *va, unsigned long flags, const void *caller)
@@ -2133,7 +2136,6 @@ struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
GFP_KERNEL, __builtin_return_address(0));
}
-EXPORT_SYMBOL_GPL(__get_vm_area);

struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
unsigned long start, unsigned long end,
@@ -2160,6 +2162,7 @@ struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
NUMA_NO_NODE, GFP_KERNEL,
__builtin_return_address(0));
}
+EXPORT_SYMBOL_GPL(get_vm_area);

struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags,
const void *caller)