Hello Dave,

I've applied this patch (manually, because 4/6 is not yet applied).
I have a question below.

On 5/27/20 11:17 PM, Dave Martin wrote:

Add documentation for the PR_PAC_RESET_KEYS ioctl added in Linux
5.0 for arm64.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Amit Daniel Kachhap <redacted>
Cc: Mark Rutland <mark.rutland@arm.com>

---

Since v1:

 * Clarify explicitly that PR_PAC_RESET_KEYS is redundant when combined
   with execve().

 * Move error condition details into the prctl description, to avoid
   excessive duplication while keeping keeping related pieces of text
   closer together.

 * In lieu of having a separate man page to cross reference for detailed
   guidance, cross-reference the kernel documentation.

 * Add safety warning.  This is deliberately vague, pending ongoing
   discussions with libc folks.
---
 man2/prctl.2 | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

[...]

+.IP
+.B Warning:
+Because the compiler or run-time environment
+may be using some or all of the keys,
+a successful

Things got a bit garbled here. I think the next few lines should have been 
at the end.

+.IP
+For more information, see the kernel source file
+.I Documentation/arm64/pointer\-authentication.rst
+.\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed
+(or
+.I Documentation/arm64/pointer\-authentication.txt
+before Linux 5.3).
+.B PR_PAC_RESET_KEYS
+may crash the calling process.
+The conditions for using it safely are complex and system-dependent.
+Don't use it unless you know what you are doing.

I applied the following change after your patch; is it okay?

 .IP
 .B Warning:
 Because the compiler or run-time environment
 may be using some or all of the keys,
 a successful
+may crash the calling process.
+The conditions for using it safely are complex and system-dependent.
+Don't use it unless you know what you are doing.
 .IP
 For more information, see the kernel source file
 .I Documentation/arm64/pointer\-authentication.rst

@@ -1020,9 +1023,6 @@ For more information, see the kernel source file
 .I Documentation/arm64/pointer\-authentication.txt
 before Linux 5.3).
 .B PR_PAC_RESET_KEYS
-may crash the calling process.
-The conditions for using it safely are complex and system-dependent.
-Don't use it unless you know what you are doing.
 .\" prctl PR_SET_PDEATHSIG
 .TP
 .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"

[...]

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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