When swapping pages out to disk it is necessary to save any tags that
have been set, and restore when swapping back in. Make use of the new
page flag (PG_ARCH_2, locally named PG_mte_tagged) to identify pages
with tags. When swapping out these pages the tags are stored in memory
and later restored when the pages are brought back in. Because shmem can
swap pages back in without restoring the userspace PTE it is also
necessary to add a hook for shmem.
Signed-off-by: Steven Price <steven.price@arm.com>
[catalin.marinas@arm.com: move function prototypes to mte.h]
[catalin.marinas@arm.com: drop '_tags' from arch_swap_restore_tags()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Will Deacon <will@kernel.org>
Add support for bulk setting/getting of the MTE tags in a tracee's
address space at 'addr' in the ptrace() syscall prototype. 'data' points
to a struct iovec in the tracer's address space with iov_base
representing the address of a tracer's buffer of length iov_len. The
tags to be copied to/from the tracer's buffer are stored as one tag per
byte.
On successfully copying at least one tag, ptrace() returns 0 and updates
the tracer's iov_len with the number of tags copied. In case of error,
either -EIO or -EFAULT is returned, trying to follow the ptrace() man
page.
Note that the tag copying functions are not performance critical,
therefore they lack optimisations found in typical memory copy routines.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Alan Hayward <Alan.Hayward@arm.com>
Cc: Luis Machado <luis.machado@linaro.org>
Cc: Omair Javaid <omair.javaid@linaro.org>
In preparation for ptrace() access to the prctl() value, allow calling
these functions on non-current tasks.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
The CPU resume/suspend routines only take care of the common system
registers. Restore GCR_EL1 in addition via the __cpu_suspend_exit()
function.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
The IRG, ADDG and SUBG instructions insert a random tag in the resulting
address. Certain tags can be excluded via the GCR_EL1.Exclude bitmap
when, for example, the user wants a certain colour for freed buffers.
Since the GCR_EL1 register is not accessible at EL0, extend the
prctl(PR_SET_TAGGED_ADDR_CTRL) interface to include a 16-bit field in
the first argument for controlling which tags can be generated by the
above instruction (an include rather than exclude mask). Note that by
default all non-zero tags are excluded. This setting is per-thread.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
By default, even if PROT_MTE is set on a memory range, there is no tag
check fault reporting (SIGSEGV). Introduce a set of option to the
exiting prctl(PR_SET_TAGGED_ADDR_CTRL) to allow user control of the tag
check fault mode:
PR_MTE_TCF_NONE - no reporting (default)
PR_MTE_TCF_SYNC - synchronous tag check fault reporting
PR_MTE_TCF_ASYNC - asynchronous tag check fault reporting
These options translate into the corresponding SCTLR_EL1.TCF0 bitfield,
context-switched by the kernel. Note that the kernel accesses to the
user address space (e.g. read() system call) are not checked if the user
thread tag checking mode is PR_MTE_TCF_NONE or PR_MTE_TCF_ASYNC. If the
tag checking mode is PR_MTE_TCF_SYNC, the kernel makes a best effort to
check its user address accesses, however it cannot always guarantee it.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
When the Memory Tagging Extension is enabled, two pages are identical
only if both their data and tags are identical.
Make the generic memcmp_pages() a __weak function and add an
arm64-specific implementation which returns non-zero if any of the two
pages contain valid MTE tags (PG_mte_tagged set). There isn't much
benefit in comparing the tags of two pages since these are normally used
for heap allocations and likely to differ anyway.
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Pages allocated by the kernel are not guaranteed to have the tags
zeroed, especially as the kernel does not (yet) use MTE itself. To
ensure the user can still access such pages when mapped into its address
space, clear the tags via set_pte_at(). A new page flag - PG_mte_tagged
(PG_arch_2) - is used to track pages with valid allocation tags.
Since the zero page is mapped as pte_special(), it won't be covered by
the above set_pte_at() mechanism. Clear its tags during early MTE
initialisation.
Co-developed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
The Memory Tagging Extension has two modes of notifying a tag check
fault at EL0, configurable through the SCTLR_EL1.TCF0 field:
1. Synchronous raising of a Data Abort exception with DFSC 17.
2. Asynchronous setting of a cumulative bit in TFSRE0_EL1.
Add the exception handler for the synchronous exception and handling of
the asynchronous TFSRE0_EL1.TF0 bit setting via a new TIF flag in
do_notify_resume().
On a tag check failure in user-space, whether synchronous or
asynchronous, a SIGSEGV will be raised on the faulting thread.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
