[clang] c9b1a2b - AArch64: Use SBFX instead of UBFX to extract address granule in outlined HWASan checks.

[Peter Collingbourne via cfe-commits]

Author: Peter Collingbourne
Date: 2020-10-30T12:53:15-07:00
New Revision: c9b1a2b41dca6e6734aa39833a0dab0d0a8b53d3

URL: https://github.com/llvm/llvm-project/commit/c9b1a2b41dca6e6734aa39833a0dab0d0a8b53d3
DIFF: https://github.com/llvm/llvm-project/commit/c9b1a2b41dca6e6734aa39833a0dab0d0a8b53d3.diff

LOG: AArch64: Use SBFX instead of UBFX to extract address granule in outlined HWASan checks.

In a kernel (or in general in environments where bit 55 of the address
is set) the shadow base needs to point to the end of the shadow region,
not the beginning. Bit 55 needs to be sign extended into bits 52-63
of the shadow base offset, otherwise we end up loading from an invalid
address. We can do this by using SBFX instead of UBFX.

Using SBFX should have no effect in the userspace case where bit 55
of the address is clear so we do so unconditionally. I don't think
we need a ABI version bump for this (but one will come anyway when
we switch to x20 for the shadow base register).

Differential Revision: https://reviews.llvm.org/D90424

Added: 
    

Modified: 
    clang/docs/HardwareAssistedAddressSanitizerDesign.rst
    llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
    llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll

Removed: 
    


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diff  --git a/clang/docs/HardwareAssistedAddressSanitizerDesign.rst b/clang/docs/HardwareAssistedAddressSanitizerDesign.rst
index bb612138264e..b97fbb91a43a 100644
--- a/clang/docs/HardwareAssistedAddressSanitizerDesign.rst
+++ b/clang/docs/HardwareAssistedAddressSanitizerDesign.rst
@@ -96,7 +96,7 @@ Currently, the following sequence is used:
 
   [...]
   __hwasan_check_x0_2_short_v2:
-        ubfx    x16, x0, #4, #52                        // shadow offset
+        sbfx    x16, x0, #4, #52                        // shadow offset
         ldrb    w16, [x20, x16]                         // load shadow tag
         cmp     x16, x0, lsr #56                        // extract address tag, compare with shadow tag
         b.ne    .Ltmp0                                  // jump to short tag handler on mismatch

diff  --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index dd101db1917c..006986d70456 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -348,7 +348,7 @@ void AArch64AsmPrinter::EmitHwasanMemaccessSymbols(Module &M) {
     OutStreamer->emitSymbolAttribute(Sym, MCSA_Hidden);
     OutStreamer->emitLabel(Sym);
 
-    OutStreamer->emitInstruction(MCInstBuilder(AArch64::UBFMXri)
+    OutStreamer->emitInstruction(MCInstBuilder(AArch64::SBFMXri)
                                      .addReg(AArch64::X16)
                                      .addReg(Reg)
                                      .addImm(4)

diff  --git a/llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll b/llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll
index 4042eee6d262..61fcff5433ed 100644
--- a/llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll
+++ b/llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll
@@ -38,7 +38,7 @@ declare void @llvm.hwasan.check.memaccess.shortgranules(i8*, i8*, i32)
 ; CHECK-NEXT: .weak __hwasan_check_x0_2_short_v2
 ; CHECK-NEXT: .hidden __hwasan_check_x0_2_short_v2
 ; CHECK-NEXT: __hwasan_check_x0_2_short_v2:
-; CHECK-NEXT: ubfx x16, x0, #4, #52
+; CHECK-NEXT: sbfx x16, x0, #4, #52
 ; CHECK-NEXT: ldrb w16, [x20, x16]
 ; CHECK-NEXT: cmp x16, x0, lsr #56
 ; CHECK-NEXT: b.ne .Ltmp0
@@ -69,7 +69,7 @@ declare void @llvm.hwasan.check.memaccess.shortgranules(i8*, i8*, i32)
 ; CHECK-NEXT: .weak __hwasan_check_x1_1
 ; CHECK-NEXT: .hidden __hwasan_check_x1_1
 ; CHECK-NEXT: __hwasan_check_x1_1:
-; CHECK-NEXT: ubfx x16, x1, #4, #52
+; CHECK-NEXT: sbfx x16, x1, #4, #52
 ; CHECK-NEXT: ldrb w16, [x9, x16]
 ; CHECK-NEXT: cmp x16, x1, lsr #56
 ; CHECK-NEXT: b.ne .Ltmp3