> On Oct 24, 2018, at 12:51 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
>> On Wed, Oct 24, 2018 at 8:35 AM, Michael Sammler <msammler@xxxxxxxxxxx> wrote:
>> Add the current value of the PKRU register to data available for
>> seccomp-bpf programs to work on. This allows filters based on the
>> currently enabled protection keys.
>
> As mentioned in the thread, this commit log needs to be expanded greatly. :)
>
>>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> Cc: Will Drewry <wad@xxxxxxxxxxxx>
>> Cc: linux-api@xxxxxxxxxxxxxxx
>> Signed-off-by: Michael Sammler <msammler@xxxxxxxxxxx>
>> ---
>> arch/mips/kernel/ptrace.c | 2 ++
>> arch/x86/entry/common.c | 2 ++
>> include/uapi/linux/seccomp.h | 4 ++++
>> kernel/seccomp.c | 2 ++
>> tools/testing/selftests/seccomp/seccomp_bpf.c | 4 +++-
>> 5 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
>> index e5ba56c0..07d55955 100644
>> --- a/arch/mips/kernel/ptrace.c
>> +++ b/arch/mips/kernel/ptrace.c
>> @@ -1277,6 +1277,8 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
>> for (i = 0; i < 6; i++)
>> sd.args[i] = args[i];
>> sd.instruction_pointer = KSTK_EIP(current);
>> + sd.pkru = 0;
>> + sd.reserved = 0;
>>
>> ret = __secure_computing(&sd);
>> if (ret == -1)
>> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
>> index 3b2490b8..2afa85d7 100644
>> --- a/arch/x86/entry/common.c
>> +++ b/arch/x86/entry/common.c
>> @@ -98,6 +98,8 @@ static long syscall_trace_enter(struct pt_regs *regs)
>> sd.arch = arch;
>> sd.nr = regs->orig_ax;
>> sd.instruction_pointer = regs->ip;
>> + sd.pkru = read_pkru();
>> + sd.reserved = 0;
>> #ifdef CONFIG_X86_64
>> if (arch == AUDIT_ARCH_X86_64) {
>> sd.args[0] = regs->di;
>> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
>> index 9efc0e73..e8b9ecfc 100644
>> --- a/include/uapi/linux/seccomp.h
>> +++ b/include/uapi/linux/seccomp.h
>> @@ -52,12 +52,16 @@
>> * @instruction_pointer: at the time of the system call.
>> * @args: up to 6 system call arguments always stored as 64-bit values
>> * regardless of the architecture.
>> + * @pkru: value of the pkru register
>> + * @reserved: pad the structure to a multiple of eight bytes
>> */
>> struct seccomp_data {
>> int nr;
>> __u32 arch;
>> __u64 instruction_pointer;
>> __u64 args[6];
>> + __u32 pkru;
>> + __u32 reserved;
>> };
>
> struct seccomp_data only needs to be 32-bit aligned.
On first reading, I thought the same thing. On second reading, I changed my mind: on a 32-bit kernel, the struct will be 4-byte aligned overall, whereas on a 64-bit kernel, it’ll be 8-byte aligned. This has no effect on the layout, but it affects the size.
