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arm64: mte: Allow user control of the tag check mode via prctl()

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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>
This commit is contained in:
Catalin Marinas
2019-11-27 10:30:15 +00:00
parent 51b0bff2f7
commit 1c101da8b9
5 changed files with 123 additions and 3 deletions
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6
include/uapi/linux/prctl.h
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@@ -233,6 +233,12 @@ struct prctl_mm_map {
#define PR_SET_TAGGED_ADDR_CTRL 55
#define PR_GET_TAGGED_ADDR_CTRL 56
# define PR_TAGGED_ADDR_ENABLE (1UL << 0)
/* MTE tag check fault modes */
# define PR_MTE_TCF_SHIFT 1
# define PR_MTE_TCF_NONE (0UL << PR_MTE_TCF_SHIFT)
# define PR_MTE_TCF_SYNC (1UL << PR_MTE_TCF_SHIFT)
# define PR_MTE_TCF_ASYNC (2UL << PR_MTE_TCF_SHIFT)
# define PR_MTE_TCF_MASK (3UL << PR_MTE_TCF_SHIFT)
/* Control reclaim behavior when allocating memory */
#define PR_SET_IO_FLUSHER 57