[edk2-devel] [PATCH v3 2/2] ArmPkg/ArmMmuLib: Fix ArmReplaceLiveTranslationEntry() alignment

[Marvin Häuser]

As the ASM_FUNC() macro performs a section switch, the preceding
.balign directive applies the alignment constraint to the current
location in the previous section. As the linker may not merge the
sections in-order, ArmReplaceLiveTranslationEntry() may be left
unaligned.

Replace the explicit invocation of .balign with the ASM_FUNC_ALIGN()
macro, which guarantees the alignment constraint is applied correctly.
To make sure related issues are reliably caught in the future, align the
end of the function before checking the total occupied size. This
ensures crossing a 0x200 boundary will cause a compilation error.

Reviewed-by: Leif Lindholm <quic_llindhol at quicinc.com>
Signed-off-by: Marvin Häuser <mhaeuser at posteo.de>
Cc: Leif Lindholm <quic_llindhol at quicinc.com>
Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
Cc: Sami Mujawar <sami.mujawar at arm.com>
Cc: Vitaly Cheptsov <vit9696 at protonmail.com>
---
 .../ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S      | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
index e936a5be4e11..887439bc042f 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibReplaceEntry.S
@@ -69,17 +69,16 @@
 .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,
 //  IN  UINT64  Value,
 //  IN  UINT64  Address
 //  )
-ASM_FUNC(ArmReplaceLiveTranslationEntry)
+//
+// Align this routine to a log2 upper bound of its size, so that it is
+// guaranteed not to cross a page or block boundary.
+ASM_FUNC_ALIGN(ArmReplaceLiveTranslationEntry, 0x200)
 
   // disable interrupts
   mrs   x4, daif
@@ -101,5 +100,8 @@ ASM_GLOBAL ASM_PFX(ArmReplaceLiveTranslationEntrySize)
 ASM_PFX(ArmReplaceLiveTranslationEntrySize):
   .long   . - ArmReplaceLiveTranslationEntry
 
-  // Double check that we did not overrun the assumed maximum size
+  // Double check that we did not overrun the assumed maximum size or cross a
+  // 0x200 boundary (and thus implicitly not any larger power of two, including
+  // the page size).
+  .balign 0x200
   .org    ArmReplaceLiveTranslationEntry + 0x200
-- 
2.40.0



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