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[v4,07/36] arm64/gcs: Provide copy_to_user_gcs()

Message ID 20230807-arm64-gcs-v4-7-68cfa37f9069@kernel.org
State New
Headers show
Series arm64/gcs: Provide support for GCS in userspace | expand

Commit Message

Mark Brown Aug. 7, 2023, 10 p.m. UTC
In order for EL1 to write to an EL0 GCS it must use the GCSSTTR instruction
rather than a normal STTR. Provide a copy_to_user_gcs() which does this.
Since it is not possible to store anything other than a 64 bit value the
interface is presented in terms of 64 bit values, using unsigned long
rather than u64 due to sparse.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/uaccess.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

Comments

Catalin Marinas Aug. 11, 2023, 4:36 p.m. UTC | #1
On Mon, Aug 07, 2023 at 11:00:12PM +0100, Mark Brown wrote:
> +static inline int copy_to_user_gcs(unsigned long __user *addr,
> +				   unsigned long *val,
> +				   int count)
> +{
> +	int ret = -EFAULT;
> +	int i;
> +
> +	if (access_ok((char __user *)addr, count * sizeof(u64))) {
> +		uaccess_ttbr0_enable();
> +		for (i = 0; i < count; i++) {
> +			ret = gcssttr(addr++, *val++);
> +			if (ret != 0)
> +				break;
> +		}
> +		uaccess_ttbr0_disable();
> +	}
> +
> +	return ret;
> +}

I think it makes more sense to have a put_user_gcs() of a single
element. I've only seen it used with 2 elements in the signal code but
we could as well do two put_user_gcs() calls (as we do for other stuff
that we push to the signal frame).
Mark Brown Aug. 16, 2023, 6:26 p.m. UTC | #2
On Fri, Aug 11, 2023 at 05:36:05PM +0100, Catalin Marinas wrote:
> On Mon, Aug 07, 2023 at 11:00:12PM +0100, Mark Brown wrote:
> > +static inline int copy_to_user_gcs(unsigned long __user *addr,
> > +				   unsigned long *val,
> > +				   int count)

> I think it makes more sense to have a put_user_gcs() of a single
> element. I've only seen it used with 2 elements in the signal code but
> we could as well do two put_user_gcs() calls (as we do for other stuff
> that we push to the signal frame).

Right, it's just the two element array in the signals code and the one
element for the context token in map_shadow_stack().  I can refactor to
a single read/write operation, I'd originally written it that way but I
wasn't thrilled with either writing a load of fun macros to mirror the
way vanilla put_user() is written or having code that looked very
different to the other similarly named functions were done.
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 22e10e79f56a..24aa804e95a7 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -445,6 +445,26 @@  static inline int gcssttr(unsigned long __user *addr, unsigned long val)
 	return err;
 }
 
+static inline int copy_to_user_gcs(unsigned long __user *addr,
+				   unsigned long *val,
+				   int count)
+{
+	int ret = -EFAULT;
+	int i;
+
+	if (access_ok((char __user *)addr, count * sizeof(u64))) {
+		uaccess_ttbr0_enable();
+		for (i = 0; i < count; i++) {
+			ret = gcssttr(addr++, *val++);
+			if (ret != 0)
+				break;
+		}
+		uaccess_ttbr0_disable();
+	}
+
+	return ret;
+}
+
 #endif /* CONFIG_ARM64_GCS */
 
 #endif /* __ASM_UACCESS_H */