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2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc

 kernel/Documentation/arm64/tagged-pointers.rst
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@@ -53,12 +53,25 @@
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 Preserving tags
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 ---------------
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-Non-zero tags are not preserved when delivering signals. This means that
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-signal handlers in applications making use of tags cannot rely on the
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-tag information for user virtual addresses being maintained for fields
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-inside siginfo_t. One exception to this rule is for signals raised in
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-response to watchpoint debug exceptions, where the tag information will
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-be preserved.
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+When delivering signals, non-zero tags are not preserved in
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+siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in
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+sigaction.sa_flags when the signal handler was installed. This means
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+that signal handlers in applications making use of tags cannot rely
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+on the tag information for user virtual addresses being maintained
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+in these fields unless the flag was set.
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+
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+Due to architecture limitations, bits 63:60 of the fault address
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+are not preserved in response to synchronous tag check faults
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+(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should
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+treat the values of these bits as undefined in order to accommodate
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+future architecture revisions which may preserve the bits.
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+
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+For signals raised in response to watchpoint debug exceptions, the
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+tag information will be preserved regardless of the SA_EXPOSE_TAGBITS
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+flag setting.
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+
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+Non-zero tags are never preserved in sigcontext.fault_address
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+regardless of the SA_EXPOSE_TAGBITS flag setting.
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 The architecture prevents the use of a tagged PC, so the upper byte will
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 be set to a sign-extension of bit 55 on exception return.