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When the kernel is built with CONFIG_KASAN_HW_TAGS and the CPU supports
MTE, memory accesses are checked at 16-byte granularity, and
out-of-bounds accesses can result in tag check faults. Our current
implementation of strlen() makes unaligned 16-byte accesses (within a
naturally aligned 4096-byte window), and can trigger tag check faults.
This can be seen at boot time, e.g.
| BUG: KASAN: invalid-access in __pi_strlen+0x14/0x150
| Read at addr f4ff0000c0028300 by task swapper/0/0
| Pointer tag: [f4], memory tag: [fe]
|
| CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-09550-g03c2813535a2-dirty #20
| Hardware name: linux,dummy-virt (DT)
| Call trace:
| dump_backtrace+0x0/0x1b0
| show_stack+0x1c/0x30
| dump_stack_lvl+0x68/0x84
| print_address_description+0x7c/0x2b4
| kasan_report+0x138/0x38c
| __do_kernel_fault+0x190/0x1c4
| do_tag_check_fault+0x78/0x90
| do_mem_abort+0x44/0xb4
| el1_abort+0x40/0x60
| el1h_64_sync_handler+0xb0/0xd0
| el1h_64_sync+0x78/0x7c
| __pi_strlen+0x14/0x150
| __register_sysctl_table+0x7c4/0x890
| register_leaf_sysctl_tables+0x1a4/0x210
| register_leaf_sysctl_tables+0xc8/0x210
| __register_sysctl_paths+0x22c/0x290
| register_sysctl_table+0x2c/0x40
| sysctl_init+0x20/0x30
| proc_sys_init+0x3c/0x48
| proc_root_init+0x80/0x9c
| start_kernel+0x640/0x69c
| __primary_switched+0xc0/0xc8
To fix this, we can reduce the (strlen-internal) MIN_PAGE_SIZE to 16
bytes when CONFIG_KASAN_HW_TAGS is selected. This will cause strlen() to
align the base pointer downwards to a 16-byte boundary, and to discard
the additional prefix bytes without counting them. All subsequent
accesses will be 16-byte aligned 16-byte LDPs. While the comments say
the body of the loop will access 32 bytes, this is performed as two
16-byte acceses, with the second made only if the first did not
encounter a NUL byte, so the body of the loop will not over-read across
a 16-byte boundary.
No other string routines are affected. The other str*() routines will
not make any access which straddles a 16-byte boundary, and the mem*()
routines will only make acceses which straddle a 16-byte boundary when
which is entirely within the bounds of the relevant base and size
arguments.
Fixes:
|
||
---|---|---|
arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
LICENSES | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.