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arm64: update PAC description for kernel 

Remove the paragraph which has nothing to do with the kernel and
add PAC description related to kernel.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Link: https://lore.kernel.org/r/20211201034014.20048-1-Kuan-Ying.Lee@mediatek.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Kuan-Ying Lee 2021-12-01 11:40:10 +08:00 committed by Will Deacon
parent 94902d849e
commit ce39d473d1
1 changed files with 4 additions and 5 deletions
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9
Documentation/arm64/pointer-authentication.rst
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@ -53,11 +53,10 @@ The number of bits that the PAC occupies in a pointer is 55 minus the
virtual address size configured by the kernel. For example, with a
virtual address size of 48, the PAC is 7 bits wide.
Recent versions of GCC can compile code with APIAKey-based return
address protection when passed the -msign-return-address option. This
uses instructions in the HINT space (unless -march=armv8.3-a or higher
is also passed), and such code can run on systems without the pointer
authentication extension.
When ARM64_PTR_AUTH_KERNEL is selected, the kernel will be compiled
with HINT space pointer authentication instructions protecting
function returns. Kernels built with this option will work on hardware
with or without pointer authentication support.
In addition to exec(), keys can also be reinitialized to random values
using the PR_PAC_RESET_KEYS prctl. A bitmask of PR_PAC_APIAKEY,