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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen-unstable] HVM: support unaligned and page-crossing writes in the shadow emulator
# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1197743367 0
# Node ID d9ab9eb2bfee9de14a89ada78c45f365e489b232
# Parent 44a98411d230b3214be49b42e66d7c42e01ab59f
HVM: support unaligned and page-crossing writes in the shadow emulator
so that we can use it to support guests that clear CR0.WP.
Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
---
xen/arch/x86/mm/shadow/multi.c | 330 +++++++++++++++++++++++----------------
xen/arch/x86/mm/shadow/private.h | 20 +-
xen/include/asm-x86/hvm/hvm.h | 2
3 files changed, 216 insertions(+), 136 deletions(-)
diff -r 44a98411d230 -r d9ab9eb2bfee xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c Sat Dec 15 18:26:52 2007 +0000
+++ b/xen/arch/x86/mm/shadow/multi.c Sat Dec 15 18:29:27 2007 +0000
@@ -61,12 +61,6 @@
* and if we do flush, re-do the walk. If anything has changed, then
* pause all the other vcpus and do the walk *again*.
*
- * WP DISABLED
- * Consider how to implement having the WP bit of CR0 set to 0.
- * Since we need to be able to cause write faults to pagetables, this might
- * end up looking like not having the (guest) pagetables present at all in
- * HVM guests...
- *
* PSE disabled / PSE36
* We don't support any modes other than PSE enabled, PSE36 disabled.
* Neither of those would be hard to change, but we'd need to be able to
@@ -219,11 +213,17 @@ static uint32_t mandatory_flags(struct v
/* 1 1 1 0 */ _PAGE_PRESENT|_PAGE_USER|_PAGE_NX_BIT,
/* 1 1 1 1 */ _PAGE_PRESENT|_PAGE_RW|_PAGE_USER|_PAGE_NX_BIT,
};
- uint32_t f = flags[(pfec & 0x1f) >> 1];
+
/* Don't demand not-NX if the CPU wouldn't enforce it. */
if ( !guest_supports_nx(v) )
- f &= ~_PAGE_NX_BIT;
- return f;
+ pfec &= ~PFEC_insn_fetch;
+
+ /* Don't demand R/W if the CPU wouldn't enforce it. */
+ if ( is_hvm_vcpu(v) && unlikely(!hvm_wp_enabled(v))
+ && !(pfec & PFEC_user_mode) )
+ pfec &= ~PFEC_write_access;
+
+ return flags[(pfec & 0x1f) >> 1];
}
/* Modify a guest pagetable entry to set the Accessed and Dirty bits.
@@ -262,7 +262,8 @@ static uint32_t set_ad_bits(void *guest_
* from any guest PT pages we see, as we will be shadowing them soon
* and will rely on the contents' not having changed.
*
- * Returns 0 for success or non-zero if the walk did not complete.
+ * Returns 0 for success, or the set of permission bits that we failed on
+ * if the walk did not complete.
* N.B. This is different from the old return code but almost no callers
* checked the old return code anyway.
*/
@@ -2717,8 +2718,9 @@ static int sh_page_fault(struct vcpu *v,
fetch_type_t ft = 0;
p2m_type_t p2mt;
- SHADOW_PRINTK("d:v=%u:%u va=%#lx err=%u\n",
- v->domain->domain_id, v->vcpu_id, va, regs->error_code);
+ SHADOW_PRINTK("d:v=%u:%u va=%#lx err=%u, rip=%lx\n",
+ v->domain->domain_id, v->vcpu_id, va, regs->error_code,
+ regs->rip);
perfc_incr(shadow_fault);
//
@@ -2790,7 +2792,7 @@ static int sh_page_fault(struct vcpu *v,
shadow_lock(d);
shadow_audit_tables(v);
-
+
if ( guest_walk_tables(v, va, &gw, regs->error_code, 1) != 0 )
{
perfc_incr(shadow_fault_bail_real_fault);
@@ -2882,6 +2884,16 @@ static int sh_page_fault(struct vcpu *v,
gpa = guest_walk_to_gpa(&gw);
goto mmio;
}
+
+ /* In HVM guests, we force CR0.WP always to be set, so that the
+ * pagetables are always write-protected. If the guest thinks
+ * CR0.WP is clear, we must emulate faulting supervisor writes to
+ * allow the guest to write through read-only PTEs. Emulate if the
+ * fault was a non-user write to a present page. */
+ if ( is_hvm_domain(d)
+ && unlikely(!hvm_wp_enabled(v))
+ && regs->error_code == (PFEC_write_access|PFEC_page_present) )
+ goto emulate;
perfc_incr(shadow_fault_fixed);
d->arch.paging.log_dirty.fault_count++;
@@ -3968,25 +3980,17 @@ int sh_remove_l3_shadow(struct vcpu *v,
/**************************************************************************/
/* Handling HVM guest writes to pagetables */
-/* Check that the user is allowed to perform this write.
- * Returns a mapped pointer to write to, and the mfn it's on,
- * or NULL for error. */
-static inline void * emulate_map_dest(struct vcpu *v,
- unsigned long vaddr,
- struct sh_emulate_ctxt *sh_ctxt,
- mfn_t *mfnp)
-{
- uint32_t pfec;
+/* Translate a VA to an MFN, injecting a page-fault if we fail */
+static mfn_t emulate_gva_to_mfn(struct vcpu *v,
+ unsigned long vaddr,
+ struct sh_emulate_ctxt *sh_ctxt)
+{
unsigned long gfn;
mfn_t mfn;
p2m_type_t p2mt;
-
- /* We don't emulate user-mode writes to page tables */
- if ( ring_3(sh_ctxt->ctxt.regs) )
- return NULL;
-
- /* Translate the VA, and exit with a page-fault if we fail */
- pfec = PFEC_page_present | PFEC_write_access;
+ uint32_t pfec = PFEC_page_present | PFEC_write_access;
+
+ /* Translate the VA to a GFN */
gfn = sh_gva_to_gfn(v, vaddr, &pfec);
if ( gfn == INVALID_GFN )
{
@@ -3994,84 +3998,184 @@ static inline void * emulate_map_dest(st
hvm_inject_exception(TRAP_page_fault, pfec, vaddr);
else
propagate_page_fault(vaddr, pfec);
- return NULL;
- }
-
- /* Translate the GFN */
+ return _mfn(INVALID_MFN);
+ }
+
+ /* Translate the GFN to an MFN */
mfn = gfn_to_mfn(v->domain, _gfn(gfn), &p2mt);
if ( p2m_is_ram(p2mt) )
{
ASSERT(mfn_valid(mfn));
- *mfnp = mfn;
v->arch.paging.last_write_was_pt = !!sh_mfn_is_a_page_table(mfn);
- return sh_map_domain_page(mfn) + (vaddr & ~PAGE_MASK);
+ return mfn;
+ }
+
+ return _mfn(INVALID_MFN);
+}
+
+/* Check that the user is allowed to perform this write.
+ * Returns a mapped pointer to write to, or NULL for error. */
+static void * emulate_map_dest(struct vcpu *v,
+ unsigned long vaddr,
+ u32 bytes,
+ struct sh_emulate_ctxt *sh_ctxt)
+{
+ unsigned long offset;
+ void *map = NULL;
+
+ /* We don't emulate user-mode writes to page tables */
+ if ( ring_3(sh_ctxt->ctxt.regs) )
+ return NULL;
+
+ sh_ctxt->mfn1 = emulate_gva_to_mfn(v, vaddr, sh_ctxt);
+ if ( !mfn_valid(sh_ctxt->mfn1) )
+ return NULL;
+
+ /* Unaligned writes mean probably this isn't a pagetable */
+ if ( vaddr & (bytes - 1) )
+ sh_remove_shadows(v, sh_ctxt->mfn1, 0, 0 /* Slow, can fail */ );
+
+ if ( likely(((vaddr + bytes - 1) & PAGE_MASK) == (vaddr & PAGE_MASK)) )
+ {
+ /* Whole write fits on a single page */
+ sh_ctxt->mfn2 = _mfn(INVALID_MFN);
+ map = sh_map_domain_page(sh_ctxt->mfn1) + (vaddr & ~PAGE_MASK);
}
else
- return NULL;
-}
-
-static int safe_not_to_verify_write(mfn_t gmfn, void *dst, void *src,
- int bytes)
-{
+ {
+ /* Cross-page emulated writes are only supported for HVM guests;
+ * PV guests ought to know better */
+ if ( !is_hvm_vcpu(v) )
+ return NULL;
+
+ /* This write crosses a page boundary. Translate the second page */
+ sh_ctxt->mfn2 = emulate_gva_to_mfn(v, (vaddr + bytes - 1) & PAGE_MASK,
+ sh_ctxt);
+ if ( !mfn_valid(sh_ctxt->mfn2) )
+ return NULL;
+
+ /* Cross-page writes mean probably not a pagetable */
+ sh_remove_shadows(v, sh_ctxt->mfn2, 0, 0 /* Slow, can fail */ );
+
+ /* Hack: we map the pages into the vcpu's LDT space, since we
+ * know that we're not going to need the LDT for HVM guests,
+ * and only HVM guests are allowed unaligned writes. */
+ ASSERT(is_hvm_vcpu(v));
+ map = (void *)LDT_VIRT_START(v);
+ offset = l1_linear_offset((unsigned long) map);
+ l1e_write(&__linear_l1_table[offset],
+ l1e_from_pfn(mfn_x(sh_ctxt->mfn1), __PAGE_HYPERVISOR));
+ l1e_write(&__linear_l1_table[offset + 1],
+ l1e_from_pfn(mfn_x(sh_ctxt->mfn2), __PAGE_HYPERVISOR));
+ flush_tlb_local();
+ map += (vaddr & ~PAGE_MASK);
+ }
+
#if (SHADOW_OPTIMIZATIONS & SHOPT_SKIP_VERIFY)
- struct page_info *pg = mfn_to_page(gmfn);
- if ( !(pg->shadow_flags & SHF_32)
- && ((unsigned long)dst & 7) == 0 )
- {
- /* Not shadowed 32-bit: aligned 64-bit writes that leave the
- * present bit unset are safe to ignore. */
- if ( (*(u64*)src & _PAGE_PRESENT) == 0
- && (*(u64*)dst & _PAGE_PRESENT) == 0 )
- return 1;
- }
- else if ( !(pg->shadow_flags & (SHF_PAE|SHF_64))
- && ((unsigned long)dst & 3) == 0 )
- {
- /* Not shadowed PAE/64-bit: aligned 32-bit writes that leave the
- * present bit unset are safe to ignore. */
- if ( (*(u32*)src & _PAGE_PRESENT) == 0
- && (*(u32*)dst & _PAGE_PRESENT) == 0 )
- return 1;
- }
-#endif
- return 0;
-}
-
+ /* Remember if the bottom bit was clear, so we can choose not to run
+ * the change through the verify code if it's still clear afterwards */
+ sh_ctxt->low_bit_was_clear = map != NULL && !(*(u8 *)map & _PAGE_PRESENT);
+#endif
+
+ return map;
+}
+
+/* Tidy up after the emulated write: mark pages dirty, verify the new
+ * contents, and undo the mapping */
+static void emulate_unmap_dest(struct vcpu *v,
+ void *addr,
+ u32 bytes,
+ struct sh_emulate_ctxt *sh_ctxt)
+{
+ u32 b1 = bytes, b2 = 0, shflags;
+
+ ASSERT(mfn_valid(sh_ctxt->mfn1));
+
+ /* If we are writing lots of PTE-aligned zeros, might want to unshadow */
+ if ( likely(bytes >= 4)
+ && (*(u32 *)addr == 0)
+ && ((unsigned long) addr & ((sizeof (guest_intpte_t)) - 1)) == 0 )
+ check_for_early_unshadow(v, sh_ctxt->mfn1);
+ else
+ reset_early_unshadow(v);
+
+ /* We can avoid re-verifying the page contents after the write if:
+ * - it was no larger than the PTE type of this pagetable;
+ * - it was aligned to the PTE boundaries; and
+ * - _PAGE_PRESENT was clear before and after the write. */
+ shflags = mfn_to_page(sh_ctxt->mfn1)->shadow_flags;
+#if (SHADOW_OPTIMIZATIONS & SHOPT_SKIP_VERIFY)
+ if ( sh_ctxt->low_bit_was_clear
+ && !(*(u8 *)addr & _PAGE_PRESENT)
+ && ((!(shflags & SHF_32)
+ /* Not shadowed 32-bit: aligned 64-bit writes that leave
+ * the present bit unset are safe to ignore. */
+ && ((unsigned long)addr & 7) == 0
+ && bytes <= 8)
+ ||
+ (!(shflags & (SHF_PAE|SHF_64))
+ /* Not shadowed PAE/64-bit: aligned 32-bit writes that
+ * leave the present bit unset are safe to ignore. */
+ && ((unsigned long)addr & 3) == 0
+ && bytes <= 4)) )
+ {
+ /* Writes with this alignment constraint can't possibly cross pages */
+ ASSERT(!mfn_valid(sh_ctxt->mfn2));
+ }
+ else
+#endif /* SHADOW_OPTIMIZATIONS & SHOPT_SKIP_VERIFY */
+ {
+ if ( unlikely(mfn_valid(sh_ctxt->mfn2)) )
+ {
+ /* Validate as two writes, one to each page */
+ b1 = PAGE_SIZE - (((unsigned long)addr) & ~PAGE_MASK);
+ b2 = bytes - b1;
+ ASSERT(b2 < bytes);
+ }
+ if ( likely(b1 > 0) )
+ sh_validate_guest_pt_write(v, sh_ctxt->mfn1, addr, b1);
+ if ( unlikely(b2 > 0) )
+ sh_validate_guest_pt_write(v, sh_ctxt->mfn2, addr + b1, b2);
+ }
+
+ paging_mark_dirty(v->domain, mfn_x(sh_ctxt->mfn1));
+
+ if ( unlikely(mfn_valid(sh_ctxt->mfn2)) )
+ {
+ unsigned long offset;
+ paging_mark_dirty(v->domain, mfn_x(sh_ctxt->mfn2));
+ /* Undo the hacky two-frame contiguous map. */
+ ASSERT(((unsigned long) addr & PAGE_MASK) == LDT_VIRT_START(v));
+ offset = l1_linear_offset((unsigned long) addr);
+ l1e_write(&__linear_l1_table[offset], l1e_empty());
+ l1e_write(&__linear_l1_table[offset + 1], l1e_empty());
+ flush_tlb_all();
+ }
+ else
+ sh_unmap_domain_page(addr);
+}
int
sh_x86_emulate_write(struct vcpu *v, unsigned long vaddr, void *src,
u32 bytes, struct sh_emulate_ctxt *sh_ctxt)
{
- mfn_t mfn;
void *addr;
- int skip;
-
- if ( vaddr & (bytes-1) )
+
+ /* Unaligned writes are only acceptable on HVM */
+ if ( (vaddr & (bytes - 1)) && !is_hvm_vcpu(v) )
return X86EMUL_UNHANDLEABLE;
- ASSERT(((vaddr & ~PAGE_MASK) + bytes) <= PAGE_SIZE);
shadow_lock(v->domain);
-
- addr = emulate_map_dest(v, vaddr, sh_ctxt, &mfn);
+ addr = emulate_map_dest(v, vaddr, bytes, sh_ctxt);
if ( addr == NULL )
{
shadow_unlock(v->domain);
return X86EMUL_EXCEPTION;
}
- skip = safe_not_to_verify_write(mfn, addr, src, bytes);
memcpy(addr, src, bytes);
- if ( !skip ) sh_validate_guest_pt_write(v, mfn, addr, bytes);
-
- /* If we are writing zeros to this page, might want to unshadow */
- if ( likely(bytes >= 4) && (*(u32 *)addr == 0) && is_lo_pte(vaddr) )
- check_for_early_unshadow(v, mfn);
- else
- reset_early_unshadow(v);
-
- paging_mark_dirty(v->domain, mfn_x(mfn));
-
- sh_unmap_domain_page(addr);
+
+ emulate_unmap_dest(v, addr, bytes, sh_ctxt);
shadow_audit_tables(v);
shadow_unlock(v->domain);
return X86EMUL_OKAY;
@@ -4082,25 +4186,22 @@ sh_x86_emulate_cmpxchg(struct vcpu *v, u
unsigned long old, unsigned long new,
unsigned int bytes, struct sh_emulate_ctxt *sh_ctxt)
{
- mfn_t mfn;
void *addr;
unsigned long prev;
- int rv = X86EMUL_OKAY, skip;
-
- ASSERT(bytes <= sizeof(unsigned long));
+ int rv = X86EMUL_OKAY;
+
+ /* Unaligned writes are only acceptable on HVM */
+ if ( (vaddr & (bytes - 1)) && !is_hvm_vcpu(v) )
+ return X86EMUL_UNHANDLEABLE;
+
shadow_lock(v->domain);
- if ( vaddr & (bytes-1) )
- return X86EMUL_UNHANDLEABLE;
-
- addr = emulate_map_dest(v, vaddr, sh_ctxt, &mfn);
+ addr = emulate_map_dest(v, vaddr, bytes, sh_ctxt);
if ( addr == NULL )
{
shadow_unlock(v->domain);
return X86EMUL_EXCEPTION;
}
-
- skip = safe_not_to_verify_write(mfn, &new, &old, bytes);
switch ( bytes )
{
@@ -4113,26 +4214,14 @@ sh_x86_emulate_cmpxchg(struct vcpu *v, u
prev = ~old;
}
- if ( prev == old )
- {
- if ( !skip ) sh_validate_guest_pt_write(v, mfn, addr, bytes);
- }
- else
+ if ( prev != old )
rv = X86EMUL_CMPXCHG_FAILED;
SHADOW_DEBUG(EMULATE, "va %#lx was %#lx expected %#lx"
" wanted %#lx now %#lx bytes %u\n",
vaddr, prev, old, new, *(unsigned long *)addr, bytes);
- /* If we are writing zeros to this page, might want to unshadow */
- if ( likely(bytes >= 4) && (*(u32 *)addr == 0) && is_lo_pte(vaddr) )
- check_for_early_unshadow(v, mfn);
- else
- reset_early_unshadow(v);
-
- paging_mark_dirty(v->domain, mfn_x(mfn));
-
- sh_unmap_domain_page(addr);
+ emulate_unmap_dest(v, addr, bytes, sh_ctxt);
shadow_audit_tables(v);
shadow_unlock(v->domain);
return rv;
@@ -4144,17 +4233,17 @@ sh_x86_emulate_cmpxchg8b(struct vcpu *v,
unsigned long new_lo, unsigned long new_hi,
struct sh_emulate_ctxt *sh_ctxt)
{
- mfn_t mfn;
void *addr;
u64 old, new, prev;
- int rv = X86EMUL_OKAY, skip;
-
- if ( vaddr & 7 )
+ int rv = X86EMUL_OKAY;
+
+ /* Unaligned writes are only acceptable on HVM */
+ if ( (vaddr & 7) && !is_hvm_vcpu(v) )
return X86EMUL_UNHANDLEABLE;
shadow_lock(v->domain);
- addr = emulate_map_dest(v, vaddr, sh_ctxt, &mfn);
+ addr = emulate_map_dest(v, vaddr, 8, sh_ctxt);
if ( addr == NULL )
{
shadow_unlock(v->domain);
@@ -4163,25 +4252,12 @@ sh_x86_emulate_cmpxchg8b(struct vcpu *v,
old = (((u64) old_hi) << 32) | (u64) old_lo;
new = (((u64) new_hi) << 32) | (u64) new_lo;
- skip = safe_not_to_verify_write(mfn, &new, &old, 8);
prev = cmpxchg(((u64 *)addr), old, new);
- if ( prev == old )
- {
- if ( !skip ) sh_validate_guest_pt_write(v, mfn, addr, 8);
- }
- else
+ if ( prev != old )
rv = X86EMUL_CMPXCHG_FAILED;
- /* If we are writing zeros to this page, might want to unshadow */
- if ( *(u32 *)addr == 0 )
- check_for_early_unshadow(v, mfn);
- else
- reset_early_unshadow(v);
-
- paging_mark_dirty(v->domain, mfn_x(mfn));
-
- sh_unmap_domain_page(addr);
+ emulate_unmap_dest(v, addr, 8, sh_ctxt);
shadow_audit_tables(v);
shadow_unlock(v->domain);
return rv;
diff -r 44a98411d230 -r d9ab9eb2bfee xen/arch/x86/mm/shadow/private.h
--- a/xen/arch/x86/mm/shadow/private.h Sat Dec 15 18:26:52 2007 +0000
+++ b/xen/arch/x86/mm/shadow/private.h Sat Dec 15 18:29:27 2007 +0000
@@ -429,13 +429,6 @@ int shadow_cmpxchg_guest_entry(struct vc
#undef pagetable_from_page
#define pagetable_from_page(pg) pagetable_from_mfn(page_to_mfn(pg))
-
-#if GUEST_PAGING_LEVELS >= 3
-# define is_lo_pte(_vaddr) (((_vaddr)&0x4)==0)
-#else
-# define is_lo_pte(_vaddr) (1)
-#endif
-
static inline int
sh_mfn_is_a_page_table(mfn_t gmfn)
{
@@ -664,14 +657,23 @@ struct sh_emulate_ctxt {
struct sh_emulate_ctxt {
struct x86_emulate_ctxt ctxt;
- /* [HVM] Cache of up to 31 bytes of instruction. */
+ /* Cache of up to 31 bytes of instruction. */
uint8_t insn_buf[31];
uint8_t insn_buf_bytes;
unsigned long insn_buf_eip;
- /* [HVM] Cache of segment registers already gathered for this emulation. */
+ /* Cache of segment registers already gathered for this emulation. */
unsigned int valid_seg_regs;
struct segment_register seg_reg[6];
+
+ /* MFNs being written to in write/cmpxchg callbacks */
+ mfn_t mfn1, mfn2;
+
+#if (SHADOW_OPTIMIZATIONS & SHOPT_SKIP_VERIFY)
+ /* Special case for avoiding having to verify writes: remember
+ * whether the old value had its low bit (_PAGE_PRESENT) clear. */
+ int low_bit_was_clear:1;
+#endif
};
struct x86_emulate_ops *shadow_init_emulation(
diff -r 44a98411d230 -r d9ab9eb2bfee xen/include/asm-x86/hvm/hvm.h
--- a/xen/include/asm-x86/hvm/hvm.h Sat Dec 15 18:26:52 2007 +0000
+++ b/xen/include/asm-x86/hvm/hvm.h Sat Dec 15 18:29:27 2007 +0000
@@ -144,6 +144,8 @@ u64 hvm_get_guest_tsc(struct vcpu *v);
#define hvm_paging_enabled(v) \
(!!((v)->arch.hvm_vcpu.guest_cr[0] & X86_CR0_PG))
+#define hvm_wp_enabled(v) \
+ (!!((v)->arch.hvm_vcpu.guest_cr[0] & X86_CR0_WP))
#define hvm_pae_enabled(v) \
(hvm_paging_enabled(v) && ((v)->arch.hvm_vcpu.guest_cr[4] & X86_CR4_PAE))
#define hvm_nx_enabled(v) \
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