On 17/06/2019 14:56, Catalin Marinas wrote:

On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote:

quoted

From: Catalin Marinas <catalin.marinas@arm.com>

It is not desirable to relax the ABI to allow tagged user addresses into
the kernel indiscriminately. This patch introduces a prctl() interface
for enabling or disabling the tagged ABI with a global sysctl control
for preventing applications from enabling the relaxed ABI (meant for
testing user-space prctl() return error checking without reconfiguring
the kernel). The ABI properties are inherited by threads of the same
application and fork()'ed children but cleared on execve().

The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle
MTE-specific settings like imprecise vs precise exceptions.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

A question for the user-space folk: if an application opts in to this
ABI, would you want the sigcontext.fault_address and/or siginfo.si_addr
to contain the tag? We currently clear it early in the arm64 entry.S but
we could find a way to pass it down if needed.

to me it makes sense to keep the tag in si_addr / fault_address.

but i don't know in detail how those fields are used currently.

keeping the tag is certainly useful for MTE to debug wrong tag
failures unless there is a separate mechanism for that.

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