On Mon, Dec 11, 2023 at 06:49:37PM +0000, Catalin Marinas wrote:
On Fri, Nov 24, 2023 at 04:34:59PM +0000, Joey Gouly wrote:
@@ -211,11 +212,24 @@ init_new_context(struct task_struct *tsk, struct mm_struct *mm) { atomic64_set(&mm->context.id, 0); refcount_set(&mm->context.pinned, 0);
- // pkey 0 is the default, so always reserve it.
- mm->context.pkey_allocation_map = 0x1;
Nit: use /* */ style comments.
@@ -151,7 +170,9 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
- PTE_VALID bit set.
*/ #define pte_access_permitted(pte, write) \
- (((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER)) && (!(write) || pte_write(pte)))
- (((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER)) && \
(!(write) || pte_write(pte)) && \por_el0_allows_pkey(FIELD_GET(PTE_PO_IDX_MASK, pte_val(pte)), write, false))Do not change pte_access_permitted(), just let it handle the base permissions. This check is about the mm tables, not some current POR_EL0 setting of the thread.
As an example, with this change Linux may decide not to clear the MTE tags just because the current POR_EL0 says no-access. The thread subsequently changes POR_EL0 and it can read the stale tags.
I haven't checked what x86 and powerpc do here. There may be some implications on GUP but I'd rather ignore POE for this case.
There are tests in tools/testing/selftests/mm/protection_keys.c test_kernel_gup_of_access_disabled_region etc, that explicitly check GUP is affected by pkeys. So if we didn't modify pte_access_permitted() it would fail the test and work differently than the other architectures. For MTE/__sync_cache_and_tags, I think could add a pte_access_permitted_no_poe().
#define pmd_access_permitted(pmd, write) \ (pte_access_permitted(pmd_pte(pmd), (write))) #define pud_access_permitted(pud, write) \ diff --git a/arch/arm64/include/asm/pkeys.h b/arch/arm64/include/asm/pkeys.h index 5761fb48fd53..a80c654da93d 100644 --- a/arch/arm64/include/asm/pkeys.h +++ b/arch/arm64/include/asm/pkeys.h
[...]
static inline int execute_only_pkey(struct mm_struct *mm) {
- // Execute-only mappings are handled by EPAN/FEAT_PAN3.
- WARN_ON_ONCE(!cpus_have_final_cap(ARM64_HAS_EPAN));
- return -1;
}
Why the WARN_ON_ONCE() here? It will trigger if the user asks for PROT_EXEC and I can't see any subsequent patch that changes the core code not to call it. I think we need some arch_has_execute_only_pkey() to avoid going on this path. Our arch would support exec-only with any pkey.
This would warn if you somehow had a CPU with FEAT_POE but not FEAT_PAN3. So I don't really need the WARN() here, if the CPU supports FEAT_POE it should also support FEAT_PAN3. Arm v8.7 made FEAT_PAN3 mandatory.
@@ -1490,6 +1491,38 @@ void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr, pte #ifdef CONFIG_ARCH_HAS_PKEYS int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val) {
- return -ENOSPC;
- u64 new_por = POE_RXW;
- u64 old_por;
- u64 pkey_shift;
- if (!arch_pkeys_enabled())
return -ENOSPC;- /*
* This code should only be called with valid 'pkey'* values originating from in-kernel users. Complain* if a bad value is observed.*/- if (WARN_ON_ONCE(pkey >= arch_max_pkey()))
return -EINVAL;- /* Set the bits we need in POR: */
- if (init_val & PKEY_DISABLE_ACCESS)
new_por = POE_X;Does PKEY_DISABLE_ACCESS mean allow execute? Or does x86 not have a way to disable execution?
As I understand it X86 can either disable Read and Write or disable Write. No way to disable execution.
The man page says: PKEY_DISABLE_ACCESS Disable all data access to memory covered by the returned protection key.
- else if (init_val & PKEY_DISABLE_WRITE)
new_por = POE_RX;- /* Shift the bits in to the correct place in POR for pkey: */
- pkey_shift = pkey * POR_BITS_PER_PKEY;
- new_por <<= pkey_shift;
- /* Get old POR and mask off any old bits in place: */
- old_por = read_sysreg_s(SYS_POR_EL0);
- old_por &= ~(POE_MASK << pkey_shift);
- /* Write old part along with new part: */
- write_sysreg_s(old_por | new_por, SYS_POR_EL0);
- return 0;
} #endif
Thanks, Joey