From: Ira Weiny ira.weiny@intel.com
While evaluating the possibility of defining a new type for pkeys within the kernel I found a couple of minor bugs.
Because these patches clean up the return codes from system calls I'm sending this out RFC hoping that users will speak up if anything breaks.
I'm not too concerned about pkey_free() because it is unlikely that anyone is checking the return code. Interestingly enough, glibc recommends not calling pkey_free() because it does not change the access rights to the key and may be subsequently allocated again.[1][2]
The pkey_alloc() is more concerning. However, I checked the Chrome source and it does not differentiate among the return codes and maps all errors into kNoMemoryProtectionKey.
glibc says it returns ENOSYS if the system does not support pkeys but I don't see where ENOSYS is returned? AFAICS it just returns what the kernel returns. So it is probably up to user of glibc.
In addition I've enhanced the pkey tests to verify and test the changes.
Thanks to Rick Edgecombe and Sohil Mehta for internal review.
[1] Quote from manual/memory.texi:
Calling this function does not change the access rights of the freed protection key. The calling thread and other threads may retain access to it, even if it is subsequently allocated again. For this reason, it is not recommended to call the @code{pkey_free} function.
[2] PKS had a similar issue and went to statically allocated keys instead.
Ira Weiny (6): testing/pkeys: Add command line options testing/pkeys: Don't use uninitialized variable testing/pkeys: Add additional test for pkey_alloc() pkeys: Lift pkey hardware check for pkey_alloc() pkeys: Up level pkey_free() checks pkeys: Change mm_pkey_free() to void
arch/powerpc/include/asm/pkeys.h | 18 ++--- arch/x86/include/asm/pkeys.h | 7 +- include/linux/pkeys.h | 5 +- mm/mprotect.c | 13 +++- tools/testing/selftests/vm/pkey-helpers.h | 7 +- tools/testing/selftests/vm/protection_keys.c | 75 +++++++++++++++++--- 6 files changed, 86 insertions(+), 39 deletions(-)
base-commit: 874c8ca1e60b2c564a48f7e7acc40d328d5c8733