[PATCH] D70762: scudo: Add initial memory tagging support.

[Kevin Brodsky via Phabricator via llvm-commits]

kevin.brodsky added inline comments.


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Comment at: compiler-rt/lib/scudo/standalone/memtag.h:30
+  return (getauxval(AT_HWCAP2) & HWCAP2_MTE) &&
+         (prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) & PR_MTE_TCF_MASK) !=
+             PR_MTE_TCF_NONE;
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I wonder if this is really a good thing. If libc fails to enable tag checking before the allocator is initialised (which is quite possible, given that until recently `malloc()` was called very early in Bionic's libc_init), then Scudo will not tag anything. Wouldn't it be possible instead to explicitly ask Scudo to use tagging when it is initialised? This would also be more consistent with the `malloc_disable_memory_tagging()` interface: Scudo does not take care of enabling / disabling tag checking, so arguably it shouldn't check if it is enabled either.


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Comment at: compiler-rt/lib/scudo/standalone/memtag.h:76
+        [ End ] "=&r"(End)
+      : [ Ptr ] "r"(Ptr), [ Size ] "r"(Size));
+}
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Since this asm statement is modifying memory, is it safe to use it without a "memory" clobber? It certainly isn't safe in general. Same comment for the other asm statements that use `st*g`.


Repository:
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  https://reviews.llvm.org/D70762/new/

https://reviews.llvm.org/D70762