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88fe352934
Khalid Aziz says:
====================
Application Data Integrity feature introduced by SPARC M7
V12 changes:
This series is same as v10 and v11 and was simply rebased on 4.16-rc2
kernel and patch 11 was added to update signal delivery code to use the
new helper functions added by Eric Biederman. Can mm maintainers please
review patches 2, 7, 8 and 9 which are arch independent, and
include/linux/mm.h and mm/ksm.c changes in patch 10 and ack these if
everything looks good?
SPARC M7 processor adds additional metadata for memory address space
that can be used to secure access to regions of memory. This additional
metadata is implemented as a 4-bit tag attached to each cacheline size
block of memory. A task can set a tag on any number of such blocks.
Access to such block is granted only if the virtual address used to
access that block of memory has the tag encoded in the uppermost 4 bits
of VA. Since sparc processor does not implement all 64 bits of VA, top 4
bits are available for ADI tags. Any mismatch between tag encoded in VA
and tag set on the memory block results in a trap. Tags are verified in
the VA presented to the MMU and tags are associated with the physical
page VA maps on to. If a memory page is swapped out and page frame gets
reused for another task, the tags are lost and hence must be saved when
swapping or migrating the page.
A userspace task enables ADI through mprotect(). This patch series adds
a page protection bit PROT_ADI and a corresponding VMA flag
VM_SPARC_ADI. VM_SPARC_ADI is used to trigger setting TTE.mcd bit in the
sparc pte that enables ADI checking on the corresponding page. MMU
validates the tag embedded in VA for every page that has TTE.mcd bit set
in its pte. After enabling ADI on a memory range, the userspace task can
set ADI version tags using stxa instruction with ASI_MCD_PRIMARY or
ASI_MCD_ST_BLKINIT_PRIMARY ASI.
Once userspace task calls mprotect() with PROT_ADI, kernel takes
following overall steps:
1. Find the VMAs covering the address range passed in to mprotect and
set VM_SPARC_ADI flag. If address range covers a subset of a VMA, the
VMA will be split.
2. When a page is allocated for a VA and the VMA covering this VA has
VM_SPARC_ADI flag set, set the TTE.mcd bit so MMU will check the
vwersion tag.
3. Userspace can now set version tags on the memory it has enabled ADI
on. Userspace accesses ADI enabled memory using a virtual address that
has the version tag embedded in the high bits. MMU validates this
version tag against the actual tag set on the memory. If tag matches,
MMU performs the VA->PA translation and access is granted. If there is a
mismatch, hypervisor sends a data access exception or precise memory
corruption detected exception depending upon whether precise exceptions
are enabled or not (controlled by MCDPERR register). Kernel sends
SIGSEGV to the task with appropriate si_code.
4. If a page is being swapped out or migrated, kernel must save any ADI
tags set on the page. Kernel maintains a page worth of tag storage
descriptors. Each descriptors pointsto a tag storage space and the
address range it covers. If the page being swapped out or migrated has
ADI enabled on it, kernel finds a tag storage descriptor that covers the
address range for the page or allocates a new descriptor if none of the
existing descriptors cover the address range. Kernel saves tags from the
page into the tag storage space descriptor points to.
5. When the page is swapped back in or reinstantiated after migration,
kernel restores the version tags on the new physical page by retrieving
the original tag from tag storage pointed to by a tag storage descriptor
for the virtual address range for new page.
User task can disable ADI by calling mprotect() again on the memory
range with PROT_ADI bit unset. Kernel clears the VM_SPARC_ADI flag in
VMAs, merges adjacent VMAs if necessary, and clears TTE.mcd bit in the
corresponding ptes.
IOMMU does not support ADI checking. Any version tags embedded in the
top bits of VA meant for IOMMU, are cleared and replaced with sign
extension of the first non-version tag bit (bit 59 for SPARC M7) for
IOMMU addresses.
This patch series adds support for this feature in 11 patches:
Patch 1/11
Tag mismatch on access by a task results in a trap from hypervisor as
data access exception or a precide memory corruption detected
exception. As part of handling these exceptions, kernel sends a
SIGSEGV to user process with special si_code to indicate which fault
occurred. This patch adds three new si_codes to differentiate between
various mismatch errors.
Patch 2/11
When a page is swapped or migrated, metadata associated with the page
must be saved so it can be restored later. This patch adds a new
function that saves/restores this metadata when updating pte upon a
swap/migration.
Patch 3/11
SPARC M7 processor adds new fields to control registers to support ADI
feature. It also adds a new exception for precise traps on tag
mismatch. This patch adds definitions for the new control register
fields, new ASIs for ADI and an exception handler for the precise trap
on tag mismatch.
Patch 4/11
New hypervisor fault types were added by sparc M7 processor to support
ADI feature. This patch adds code to handle these fault types for data
access exception handler.
Patch 5/11
When ADI is in use for a page and a tag mismatch occurs, processor
raises "Memory corruption Detected" trap. This patch adds a handler
for this trap.
Patch 6/11
ADI usage is governed by ADI properties on a platform. These
properties are provided to kernel by firmware. Thsi patch adds new
auxiliary vectors that provide these values to userpsace.
Patch 7/11
arch_validate_prot() is used to validate the new protection bits asked
for by the userspace app. Validating protection bits may need the
context of address space the bits are being applied to. One such
example is PROT_ADI bit on sparc processor that enables ADI protection
on an address range. ADI protection applies only to addresses covered
by physical RAM and not other PFN mapped addresses or device
addresses. This patch adds "address" to the parameters being passed to
arch_validate_prot() to provide that context.
Patch 8/11
When protection bits are changed on a page, kernel carries forward all
protection bits except for read/write/exec. Additional code was added
to allow kernel to clear PKEY bits on x86 but this requirement to
clear other bits is not unique to x86. This patch extends the existing
code to allow other architectures to clear any other protection bits
as well on protection bit change.
Patch 9/11
When a processor supports additional metadata on memory pages, that
additional metadata needs to be copied to new memory pages when those
pages are moved. This patch allows architecture specific code to
replace the default copy_highpage() routine with arch specific
version that copies the metadata as well besides the data on the page.
Patch 10/11
This patch adds support for a user space task to enable ADI and enable
tag checking for subsets of its address space. As part of enabling
this feature, this patch adds to support manipulation of precise
exception for memory corruption detection, adds code to save and
restore tags on page swap and migration, and adds code to handle ADI
tagged addresses for DMA.
Patch 11/11
Update signal delivery code in arch/sparc/kernel/traps_64.c to use
the new helper function force_sig_fault() added by commit
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