[llvm-dev] [MTE] Tagging Globals

[Zhaoshi Zheng via llvm-dev]

Thanks for the update, Phillips.

Yes, please add me, Stephen and Ana (CCed) to Phabricator reviews.

Zhaoshi

From: Mitch Phillips <mitchp at google.com>
Sent: Tuesday, July 14, 2020 19:10
To: Zhaoshi Zheng <zhaoshiz at quicinc.com>
Cc: llvm-dev at lists.llvm.org; Stephen Long <steplong at quicinc.com>
Subject: [EXT] Re: [llvm-dev] [MTE] Tagging Globals

Hi Zhaoshi,

Currently there's no global tagging instrumentation for MTE. We have a good idea about the implementation's design - but no patches are ready to be shared at this stage.

If you'd like - I'd be more than happy to CC yourself and Stephen on any Phabricator reviews :).

On Tue, Jul 14, 2020 at 5:04 PM Zhaoshi Zheng via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hello,

We’re evaluating memory tagging (MTE) on some internal workloads.

We noticed that stack variables are tagged by an instrumentation pass and heap objects are handled by the allocator (Scudo).

How about global variables? We tried a simple case using -march=armv8a+memtag -fsanitize=memtag, but found no tagging:

Are we missing anything or tagging globals is still in progress?

int global_array[16];

int main(int argc, char **argv) {
  global_array[1] = 0;
  return global_array[argc + 16];  // BOOM
}

clang++ -O1 --target=aarch64-linux -march=armv8.5a+memtag -fsanitize=memtag test.cpp -S -o test.s

main:                                   // @main
.Lmain$local:
// %bb.0:                               // %entry
        adrp    x8, global_array
        add     x8, x8, :lo12:global_array
        str     wzr, [x8, #4]
        add     x8, x8, w0, sxtw #2
        ldr     w0, [x8, #64]
        ret
.Lfunc_end0:
        .size   main, .Lfunc_end0-main

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