Hi Szabolcs,

On Fri, May 31, 2024 at 03:57:07PM +0100, Szabolcs Nagy wrote:

The 05/03/2024 14:01, Joey Gouly wrote:

quoted

Implement the PKEYS interface, using the Permission Overlay Extension.

...

quoted

+#ifdef CONFIG_ARCH_HAS_PKEYS
+int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val)
+{
+	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;
+	else if (init_val & PKEY_DISABLE_WRITE)
+		new_por = POE_RX;
+

given that the architecture allows r,w,x permissions to be
set independently, should we have a 'PKEY_DISABLE_EXEC' or
similar api flag?

(on other targets it can be some invalid value that fails)

I didn't think about the best way to do that yet. PowerPC has a PKEY_DISABLE_EXECUTE.

We could either make that generic, and X86 has to error if it sees that bit, or
we add a arch-specific PKEY_DISABLE_EXECUTE like PowerPC.

A user can still set it by interacting with the register directly, but I guess
we want something for the glibc interface..

Dave, any thoughts here?

quoted

+	/* 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

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