On 23/10/2024 18:51, Dave Hansen wrote:
On 10/23/24 08:05, Kevin Brodsky wrote: ...> diff --git a/tools/testing/selftests/mm/pkey-x86.h b/tools/testing/selftests/mm/pkey-x86.h
index 5f28e26a2511..53ed9a336ffe 100644 --- a/tools/testing/selftests/mm/pkey-x86.h +++ b/tools/testing/selftests/mm/pkey-x86.h @@ -34,6 +34,8 @@ #define PAGE_SIZE 4096 #define MB (1<<20) +#define PKEY_ALLOW_NONE 0x55555555
Hi Kevin,
Looking at this in context, I think "PKEY_ALLOW_NONE" is not a great name. On one hand, we have:
PKEY_DISABLE_ACCESS PKEY_DISABLE_WRITE
which are values for *A* pkey.
But PKEY_ALLOW_NONE is a whole register value and spans permissions for many keys. We don't want folks trying to do something like:
pkey_alloc(flags, PKEY_ALLOW_NONE);
If I were naming it in x86 code, I'd probably call it:
PKRU_ALLOW_NONE
or something.
I agree, the naming is not ideal, I lacked inspiration! Maybe PKEY_REG_ALLOW_NONE to remain generic?
static inline void __page_o_noops(void) { /* 8-bytes of instruction * 512 bytes = 1 page */ diff --git a/tools/testing/selftests/mm/pkey_sighandler_tests.c b/tools/testing/selftests/mm/pkey_sighandler_tests.c index a8088b645ad6..b5e1767ee5d9 100644 --- a/tools/testing/selftests/mm/pkey_sighandler_tests.c +++ b/tools/testing/selftests/mm/pkey_sighandler_tests.c @@ -37,6 +37,8 @@ pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; pthread_cond_t cond = PTHREAD_COND_INITIALIZER; siginfo_t siginfo = {0}; +static u64 pkey_reg_no_access;
Ideally, this would be a real const or a #define because it really is static. Right? Or is there something dynamic about the ARM implementation's value?
It isn't dynamic no, the issue is that on architectures where pkeys restrict execution we need to allow X for pkey 0. Of course it would be possible to define PKEY_REG_ALLOW_ALL in such a way that X is allowed for pkey 0, but I was concerned this might be misleading. No strong opinion either way, happy to make it purely a macro, maybe with a better name?
...
* Setup alternate signal stack, which should be pkey_mprotect()ed by@@ -142,7 +145,8 @@ static void *thread_segv_maperr_ptr(void *ptr) syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0); /* Disable MPK 0. Only MPK 1 is enabled. */
- __write_pkey_reg(0x55555551);
- pkey_reg = set_pkey_bits(pkey_reg_no_access, 1, 0);
- __write_pkey_reg(pkey_reg);
The existing magic numbers are not great, but could we do:
#define PKEY_ALLOW_ALL 0x0
So that this can be written like this:
pkey_reg = PKRU_ALLOW_NONE; pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL);
That would get rid of the magic '0'.
Definitely better yes. But how about using Yury's uapi addition, PKEY_UNRESTRICTED [1]?
[1] https://lore.kernel.org/all/20241022120128.359652-1-yury.khrustalev@arm.com/
/* Segfault */ *bad = 1; @@ -240,6 +244,7 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void) int pkey; int parent_pid = 0; int child_pid = 0;
- u64 pkey_reg;
sa.sa_flags = SA_SIGINFO | SA_ONSTACK; @@ -257,7 +262,9 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void) assert(stack != MAP_FAILED); /* Allow access to MPK 0 and MPK 1 */
- __write_pkey_reg(0x55555550);
- pkey_reg = set_pkey_bits(pkey_reg_no_access, 0, 0);
- pkey_reg = set_pkey_bits(pkey_reg, 1, 0);
- __write_pkey_reg(pkey_reg);
... and using the pattern from above, this is quite a bit more readable:
pkey_reg = PKRU_ALLOW_NONE; pkey_reg = set_pkey_bits(pkey_reg, 0, PKEY_ALLOW_ALL); pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL);
...
- /* Only allow X for MPK 0 and nothing for other keys */
- pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0,
PKEY_DISABLE_ACCESS);If the comment says "only allow X", then I'd expect the code to say:
pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0, PKEY_X);
... or something similar.
I could #define PKEY_X PKEY_DISABLE_ACCESS but is the mixture of negative and positive polarity really helping? We cannot define PKEY_R and PKEY_W so that (for instance) PKEY_R | PKEY_X does what it says. Having to use PKEY_DISABLE_ACCESS to mean "X only" is not ideal, but this is what userspace already has to do.
Either way if we define PKEY_REG_ALLOW_NONE or similar to allow X for pkey 0 as suggested then this will go.
Thanks for the review!
Kevin