ArmPkg/ArmMmuLib: Disable and re-enable MMU only when needed

When updating a page table descriptor in a way that requires break
before make, we temporarily disable the MMU to ensure that we don't
unmap the memory region that the code itself is executing from.

However, this is a condition we can check in a straight-forward manner,
and if the regions are disjoint, we don't have to bother with the MMU
controls, and we can just perform an ordinary break before make.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>

2 files changed, 119 insertions, 26 deletions

diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
index 34f1031c4d..4d75788ed2 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
@@ -18,6 +18,17 @@
 #include <Library/ArmMmuLib.h>

 #include <Library/BaseLib.h>

 #include <Library/DebugLib.h>

+#include <Library/HobLib.h>

+

+STATIC

+VOID (

+  EFIAPI  *mReplaceLiveEntryFunc

+  )(

+    IN  UINT64  *Entry,

+    IN  UINT64  Value,

+    IN  UINT64  RegionStart,

+    IN  BOOLEAN DisableMmu

+    ) = ArmReplaceLiveTranslationEntry;

 

 STATIC

 UINT64

@@ -83,14 +94,40 @@ ReplaceTableEntry (
   IN  UINT64   *Entry,

   IN  UINT64   Value,

   IN  UINT64   RegionStart,

+  IN  UINT64   BlockMask,

   IN  BOOLEAN  IsLiveBlockMapping

   )

 {

-  if (!ArmMmuEnabled () || !IsLiveBlockMapping) {

+  BOOLEAN  DisableMmu;

+

+  //

+  // Replacing a live block entry with a table entry (or vice versa) requires a

+  // break-before-make sequence as per the architecture. This means the mapping

+  // must be made invalid and cleaned from the TLBs first, and this is a bit of

+  // a hassle if the mapping in question covers the code that is actually doing

+  // the mapping and the unmapping, and so we only bother with this if actually

+  // necessary.

+  //

+

+  if (!IsLiveBlockMapping || !ArmMmuEnabled ()) {

+    // If the mapping is not a live block mapping, or the MMU is not on yet, we

+    // can simply overwrite the entry.

     *Entry = Value;

     ArmUpdateTranslationTableEntry (Entry, (VOID *)(UINTN)RegionStart);

   } else {

-    ArmReplaceLiveTranslationEntry (Entry, Value, RegionStart);

+    // If the mapping in question does not cover the code that updates the

+    // entry in memory, or the entry that we are intending to update, we can

+    // use an ordinary break before make. Otherwise, we will need to

+    // temporarily disable the MMU.

+    DisableMmu = FALSE;

+    if ((((RegionStart ^ (UINTN)ArmReplaceLiveTranslationEntry) & ~BlockMask) == 0) ||

+        (((RegionStart ^ (UINTN)Entry) & ~BlockMask) == 0))

+    {

+      DisableMmu = TRUE;

+      DEBUG ((DEBUG_WARN, "%a: splitting block entry with MMU disabled\n", __FUNCTION__));

+    }

+

+    ArmReplaceLiveTranslationEntry (Entry, Value, RegionStart, DisableMmu);

   }

 }

 

@@ -155,12 +192,13 @@ IsTableEntry (
 STATIC

 EFI_STATUS

 UpdateRegionMappingRecursive (

-  IN  UINT64  RegionStart,

-  IN  UINT64  RegionEnd,

-  IN  UINT64  AttributeSetMask,

-  IN  UINT64  AttributeClearMask,

-  IN  UINT64  *PageTable,

-  IN  UINTN   Level

+  IN  UINT64   RegionStart,

+  IN  UINT64   RegionEnd,

+  IN  UINT64   AttributeSetMask,

+  IN  UINT64   AttributeClearMask,

+  IN  UINT64   *PageTable,

+  IN  UINTN    Level,

+  IN  BOOLEAN  TableIsLive

   )

 {

   UINTN       BlockShift;

@@ -170,6 +208,7 @@ UpdateRegionMappingRecursive (
   UINT64      EntryValue;

   VOID        *TranslationTable;

   EFI_STATUS  Status;

+  BOOLEAN     NextTableIsLive;

 

   ASSERT (((RegionStart | RegionEnd) & EFI_PAGE_MASK) == 0);

 

@@ -198,7 +237,14 @@ UpdateRegionMappingRecursive (
     // the next level. No block mappings are allowed at all at level 0,

     // so in that case, we have to recurse unconditionally.

     //

+    // One special case to take into account is any region that covers the page

+    // table itself: if we'd cover such a region with block mappings, we are

+    // more likely to end up in the situation later where we need to disable

+    // the MMU in order to update page table entries safely, so prefer page

+    // mappings in that particular case.

+    //

     if ((Level == 0) || (((RegionStart | BlockEnd) & BlockMask) != 0) ||

+        ((Level < 3) && (((UINT64)PageTable & ~BlockMask) == RegionStart)) ||

         IsTableEntry (*Entry, Level))

     {

       ASSERT (Level < 3);

@@ -234,7 +280,8 @@ UpdateRegionMappingRecursive (
                      *Entry & TT_ATTRIBUTES_MASK,

                      0,

                      TranslationTable,

-                     Level + 1

+                     Level + 1,

+                     FALSE

                      );

           if (EFI_ERROR (Status)) {

             //

@@ -246,8 +293,11 @@ UpdateRegionMappingRecursive (
             return Status;

           }

         }

+

+        NextTableIsLive = FALSE;

       } else {

         TranslationTable = (VOID *)(UINTN)(*Entry & TT_ADDRESS_MASK_BLOCK_ENTRY);

+        NextTableIsLive  = TableIsLive;

       }

 

       //

@@ -259,7 +309,8 @@ UpdateRegionMappingRecursive (
                  AttributeSetMask,

                  AttributeClearMask,

                  TranslationTable,

-                 Level + 1

+                 Level + 1,

+                 NextTableIsLive

                  );

       if (EFI_ERROR (Status)) {

         if (!IsTableEntry (*Entry, Level)) {

@@ -282,7 +333,8 @@ UpdateRegionMappingRecursive (
           Entry,

           EntryValue,

           RegionStart,

-          IsBlockEntry (*Entry, Level)

+          BlockMask,

+          TableIsLive && IsBlockEntry (*Entry, Level)

           );

       }

     } else {

@@ -291,7 +343,7 @@ UpdateRegionMappingRecursive (
       EntryValue |= (Level == 3) ? TT_TYPE_BLOCK_ENTRY_LEVEL3

                                  : TT_TYPE_BLOCK_ENTRY;

 

-      ReplaceTableEntry (Entry, EntryValue, RegionStart, FALSE);

+      ReplaceTableEntry (Entry, EntryValue, RegionStart, BlockMask, FALSE);

     }

   }

 

@@ -301,10 +353,11 @@ UpdateRegionMappingRecursive (
 STATIC

 EFI_STATUS

 UpdateRegionMapping (

-  IN  UINT64  RegionStart,

-  IN  UINT64  RegionLength,

-  IN  UINT64  AttributeSetMask,

-  IN  UINT64  AttributeClearMask

+  IN  UINT64   RegionStart,

+  IN  UINT64   RegionLength,

+  IN  UINT64   AttributeSetMask,

+  IN  UINT64   AttributeClearMask,

+  IN  BOOLEAN  TableIsLive

   )

 {

   UINTN  T0SZ;

@@ -321,7 +374,8 @@ UpdateRegionMapping (
            AttributeSetMask,

            AttributeClearMask,

            ArmGetTTBR0BaseAddress (),

-           GetRootTableLevel (T0SZ)

+           GetRootTableLevel (T0SZ),

+           TableIsLive

            );

 }

 

@@ -336,7 +390,8 @@ FillTranslationTable (
            MemoryRegion->VirtualBase,

            MemoryRegion->Length,

            ArmMemoryAttributeToPageAttribute (MemoryRegion->Attributes) | TT_AF,

-           0

+           0,

+           FALSE

            );

 }

 

@@ -410,7 +465,8 @@ ArmSetMemoryAttributes (
            BaseAddress,

            Length,

            PageAttributes,

-           PageAttributeMask

+           PageAttributeMask,

+           TRUE

            );

 }

 

@@ -423,7 +479,13 @@ SetMemoryRegionAttribute (
   IN  UINT64                BlockEntryMask

   )

 {

-  return UpdateRegionMapping (BaseAddress, Length, Attributes, BlockEntryMask);

+  return UpdateRegionMapping (

+           BaseAddress,

+           Length,

+           Attributes,

+           BlockEntryMask,

+           TRUE

+           );

 }

 

 EFI_STATUS

diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
index 66ebca571e..e936a5be4e 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
@@ -12,6 +12,14 @@
 

   .macro __replace_entry, el

 

+  // check whether we should disable the MMU

+  cbz   x3, .L1_\@

+

+  // clean and invalidate first so that we don't clobber

+  // adjacent entries that are dirty in the caches

+  dc    civac, x0

+  dsb   nsh

+

   // disable the MMU

   mrs   x8, sctlr_el\el

   bic   x9, x8, #CTRL_M_BIT

@@ -38,8 +46,33 @@
   // re-enable the MMU

   msr   sctlr_el\el, x8

   isb

+  b     .L2_\@

+

+.L1_\@:

+  // write invalid entry

+  str   xzr, [x0]

+  dsb   nshst

+

+  // flush translations for the target address from the TLBs

+  lsr   x2, x2, #12

+  .if   \el == 1

+  tlbi  vaae1, x2

+  .else

+  tlbi  vae\el, x2

+  .endif

+  dsb   nsh

+

+  // write updated entry

+  str   x1, [x0]

+  dsb   nshst

+

+.L2_\@:

   .endm

 

+  // Align this routine to a log2 upper bound of its size, so that it is

+  // guaranteed not to cross a page or block boundary.

+  .balign 0x200

+

 //VOID

 //ArmReplaceLiveTranslationEntry (

 //  IN  UINT64  *Entry,

@@ -53,12 +86,7 @@ ASM_FUNC(ArmReplaceLiveTranslationEntry)
   msr   daifset, #0xf

   isb

 

-  // clean and invalidate first so that we don't clobber

-  // adjacent entries that are dirty in the caches

-  dc    civac, x0

-  dsb   nsh

-

-  EL1_OR_EL2_OR_EL3(x3)

+  EL1_OR_EL2_OR_EL3(x5)

 1:__replace_entry 1

   b     4f

 2:__replace_entry 2

@@ -72,3 +100,6 @@ ASM_GLOBAL ASM_PFX(ArmReplaceLiveTranslationEntrySize)
 

 ASM_PFX(ArmReplaceLiveTranslationEntrySize):

   .long   . - ArmReplaceLiveTranslationEntry

+

+  // Double check that we did not overrun the assumed maximum size

+  .org    ArmReplaceLiveTranslationEntry + 0x200