Andy Lutomirski recently noted a probable bug in write_pkru(), but it was unclear if it was user-visible. A recent bug report in related code[1] forced me to take a look. Basically, manipulation of XSAVE state is too unstructured. get_xsave_addr() gives callers the impression they can read and write XSAVE state when there are a lot of pitfalls, like updates to xstate.features bits. As a result, more than one call site screws up the modification of PKRU in the XSAVE buffer. This series fixes that problem up and also hopefully carves out a less error-prone path that can be reused for other XSAVE features. This series: * Moves the PKRU manipulation to a more appropriate location, away from the page table code * Wraps get_xsave_addr() with more structured, less error-prone interfaces. * Conditionally hides a pkey debugfs file, eliminating the need for new runtime checks to work with the new interface. * Add a selftest to make it more likely to catch bugs like this in the future. This improved selftest catches this issue on Intel CPUs. Without the improvement, it only triggers on AMD. This has been lightly tested so far. It probably needs a tested-by from at least the AMD folks before anyone applies it. 1. https://lore.kernel.org/linux-kselftest/b2e0324a-9125-bb34-9e76-81817df27c48@xxxxxxx/ -- arch/x86/include/asm/fpu/internal.h | 8 - arch/x86/include/asm/fpu/xstate.h | 130 +++++++++++++++++++++++++++ arch/x86/include/asm/pgtable.h | 29 ------ arch/x86/include/asm/processor.h | 7 + arch/x86/kernel/cpu/common.c | 6 - arch/x86/kernel/fpu/xstate.c | 2 arch/x86/kernel/process_64.c | 1 arch/x86/kvm/svm/sev.c | 1 arch/x86/kvm/x86.c | 1 arch/x86/mm/pkeys.c | 13 +- tools/testing/selftests/vm/Makefile | 4 tools/testing/selftests/vm/pkey-x86.h | 1 tools/testing/selftests/vm/protection_keys.c | 73 +++++++++++++++ 13 files changed, 227 insertions(+), 49 deletions(-) Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: x86@xxxxxxxxxx Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Babu Moger <babu.moger@xxxxxxx> Cc: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx> Cc: Ram Pai <linuxram@xxxxxxxxxx> Cc: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
