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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
This commit is contained in:
Peter Collingbourne 2020-10-27 14:56:21 -07:00
parent 3859fc653f
commit c9b1a2b41d
3 changed files with 4 additions and 4 deletions
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2
clang/docs/HardwareAssistedAddressSanitizerDesign.rst
View File

@ -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

2
llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
View File

@ -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)

4
llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll
View File

@ -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