[PATCH v2 0/9] kasan: RISC-V support for KASAN_SW_TAGS using pointer masking

Samuel Holland
2024-10-22T02:01:23Z

This series implements support for software tag-based KASAN using the
RISC-V pointer masking extension[1], which supports 7 and/or 16-bit
tags. This implementation uses 7-bit tags, so it is compatible with
either hardware mode. Patch 4 adds supports for KASAN_SW_TAGS with tag
widths other than 8 bits.

Pointer masking is an optional ISA extension, and it must be enabled
using an SBI call to firmware on each CPU. If the SBI call fails on the
boot CPU, KASAN is globally disabled. Patch 2 adds support for boot-time
disabling of KASAN_SW_TAGS, and patch 3 adds support for runtime control
of stack tagging.

Patch 1 is an optimization that could be applied separately. It is
included here because it affects the selection of KASAN_SHADOW_OFFSET.

This implementation currently passes the KASAN KUnit test suite:

# kasan: pass:64 fail:0 skip:9 total:73
# Totals: pass:64 fail:0 skip:9 total:73
ok 1 kasan

One workaround is required to pass the vmalloc_percpu test. I have to
shrink the initial percpu area to force the use of a KASAN-tagged percpu
area in the test (depending on .config, this workaround is also needed
on arm64 without this series applied, so it is not a new issue):

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index b6321fc49159..26b97c79ad7c 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -43,7 +43,7 @@
#ifdef CONFIG_RANDOM_KMALLOC_CACHES
#define PERCPU_DYNAMIC_SIZE_SHIFT 12
#else
-#define PERCPU_DYNAMIC_SIZE_SHIFT 10
+#define PERCPU_DYNAMIC_SIZE_SHIFT 8
#endif

When running with hardware or firmware that doesn't support pointer
masking, the kernel still boots successfully:

kasan: test: Can't run KASAN tests with KASAN disabled
# kasan: # failed to initialize (-1)
not ok 1 kasan

This series can be tested by applying patch series to LLVM[2] and
QEMU[3], and using the master branch of OpenSBI[4].

[1]: https://github.com/riscv/riscv-j-extension/raw/d70011dde6c2/zjpm-spec.pdf
[2]: https://github.com/SiFiveHolland/llvm-project/commits/up/riscv64-kernel-hwasan
[3]: https://lore.kernel.org/qemu-devel/20240511101053.1875596-1-me@deliversmonkey.space/
[4]: https://github.com/riscv-software-src/opensbi/commit/1cb234b1c9ed

Changes in v2:
- Improve the explanation for how KASAN_SHADOW_END is derived
- Update the range check in kasan_non_canonical_hook()
- Split the generic and RISC-V parts of stack tag generation control
to avoid breaking bisectability
- Add a patch to call kasan_non_canonical_hook() on riscv
- Fix build error with KASAN_GENERIC
- Use symbolic definitons for SBI firmware features call
- Update indentation in scripts/Makefile.kasan
- Use kasan_params to set hwasan-generate-tags-with-calls=1

Clément Léger (1):
riscv: Add SBI Firmware Features extension definitions

Samuel Holland (8):
kasan: sw_tags: Use arithmetic shift for shadow computation
kasan: sw_tags: Check kasan_flag_enabled at runtime
kasan: sw_tags: Support outline stack tag generation
kasan: sw_tags: Support tag widths less than 8 bits
riscv: mm: Log potential KASAN shadow alias
riscv: Do not rely on KASAN to define the memory layout
riscv: Align the sv39 linear map to 16 GiB
riscv: Implement KASAN_SW_TAGS

Documentation/arch/riscv/vm-layout.rst | 10 ++---
Documentation/dev-tools/kasan.rst | 14 +++---
arch/arm64/Kconfig | 10 ++---
arch/arm64/include/asm/kasan.h | 6 ++-
arch/arm64/include/asm/memory.h | 17 ++++++-
arch/arm64/include/asm/uaccess.h | 1 +
arch/arm64/mm/kasan_init.c | 7 ++-
arch/riscv/Kconfig | 4 +-
arch/riscv/include/asm/cache.h | 4 ++
arch/riscv/include/asm/kasan.h | 29 +++++++++++-
arch/riscv/include/asm/page.h | 21 +++++++--
arch/riscv/include/asm/pgtable.h | 6 +++
arch/riscv/include/asm/sbi.h | 28 ++++++++++++
arch/riscv/include/asm/tlbflush.h | 4 +-
arch/riscv/kernel/setup.c | 6 +++
arch/riscv/kernel/smpboot.c | 8 +++-
arch/riscv/lib/Makefile | 2 +
arch/riscv/lib/kasan_sw_tags.S | 61 ++++++++++++++++++++++++++
arch/riscv/mm/fault.c | 3 ++
arch/riscv/mm/init.c | 2 +-
arch/riscv/mm/kasan_init.c | 32 +++++++++++++-
arch/riscv/mm/physaddr.c | 4 ++
include/linux/kasan-enabled.h | 15 +++----
include/linux/kasan-tags.h | 13 +++---
include/linux/kasan.h | 10 ++++-
mm/kasan/hw_tags.c | 10 -----
mm/kasan/kasan.h | 2 +
mm/kasan/report.c | 22 ++++++++--
mm/kasan/sw_tags.c | 9 ++++
mm/kasan/tags.c | 10 +++++
scripts/Makefile.kasan | 5 +++
scripts/gdb/linux/mm.py | 5 ++-
32 files changed, 313 insertions(+), 67 deletions(-)
create mode 100644 arch/riscv/lib/kasan_sw_tags.S

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2.45.1