arm64/signal: Avoid rereading context frame sizes

We need to read the sizes of the signal context frames as part of parsing
the overall signal context in parse_user_sigframe(). In the cases where we
defer frame specific parsing to other functions those functions (other
than the recently added TPIDR2 parser) reread the size and validate the
version they read, opening the possibility that the value may change.
Avoid this possibility by passing the size read in parse_user_sigframe()
through user_ctxs and referring to that.

For consistency we move the size check for the TPIDR2 context into the
TPIDR2 parsing function.

Note that for SVE, ZA and ZT contexts we still read the size again but
after this change we no longer use the value, further changes will avoid
the read.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221212-arm64-signal-cleanup-v3-4-4545c94b20ff@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: broonie

arch/arm64/kernel/signal.c

@@ -172,10 +172,15 @@ static void __user *apply_user_offset(
 
 struct user_ctxs {
 	struct fpsimd_context __user *fpsimd;
+	u32 fpsimd_size;
 	struct sve_context __user *sve;
+	u32 sve_size;
 	struct tpidr2_context __user *tpidr2;
+	u32 tpidr2_size;
 	struct za_context __user *za;
+	u32 za_size;
 	struct zt_context __user *zt;
+	u32 zt_size;
 };
 
 static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
@@ -199,14 +204,10 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
 static int restore_fpsimd_context(struct user_ctxs *user)
 {
 	struct user_fpsimd_state fpsimd;
-	__u32 size;
 	int err = 0;
 
 	/* check the size information */
-	__get_user_error(size, &user->fpsimd->head.size, err);
-	if (err)
-		return -EFAULT;
-	if (size != sizeof(struct fpsimd_context))
+	if (user->fpsimd_size != sizeof(struct fpsimd_context))
 		return -EINVAL;
 
 	/* copy the FP and status/control registers */
@@ -275,12 +276,12 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
 	struct user_fpsimd_state fpsimd;
 	struct sve_context sve;
 
+	if (user->sve_size < sizeof(*user->sve))
+		return -EINVAL;
+
 	if (__copy_from_user(&sve, user->sve, sizeof(sve)))
 		return -EFAULT;
 
-	if (sve.head.size < sizeof(*user->sve))
-		return -EINVAL;
-
 	if (sve.flags & SVE_SIG_FLAG_SM) {
 		if (!system_supports_sme())
 			return -EINVAL;
@@ -296,7 +297,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
 	if (sve.vl != vl)
 		return -EINVAL;
 
-	if (sve.head.size == sizeof(*user->sve)) {
+	if (user->sve_size == sizeof(*user->sve)) {
 		clear_thread_flag(TIF_SVE);
 		current->thread.svcr &= ~SVCR_SM_MASK;
 		current->thread.fp_type = FP_STATE_FPSIMD;
@@ -305,7 +306,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
 
 	vq = sve_vq_from_vl(sve.vl);
 
-	if (sve.head.size < SVE_SIG_CONTEXT_SIZE(vq))
+	if (user->sve_size < SVE_SIG_CONTEXT_SIZE(vq))
 		return -EINVAL;
 
 	/*
@@ -385,7 +386,9 @@ static int restore_tpidr2_context(struct user_ctxs *user)
 	u64 tpidr2_el0;
 	int err = 0;
 
-	/* Magic and size were validated deciding to call this function */
+	if (user->tpidr2_size != sizeof(*user->tpidr2))
+		return -EINVAL;
+
 	__get_user_error(tpidr2_el0, &user->tpidr2->tpidr2, err);
 	if (!err)
 		current->thread.tpidr2_el0 = tpidr2_el0;
@@ -434,23 +437,23 @@ static int restore_za_context(struct user_ctxs *user)
 	unsigned int vq;
 	struct za_context za;
 
+	if (user->za_size < sizeof(*user->za))
+		return -EINVAL;
+
 	if (__copy_from_user(&za, user->za, sizeof(za)))
 		return -EFAULT;
 
-	if (za.head.size < sizeof(*user->za))
-		return -EINVAL;
-
 	if (za.vl != task_get_sme_vl(current))
 		return -EINVAL;
 
-	if (za.head.size == sizeof(*user->za)) {
+	if (user->za_size == sizeof(*user->za)) {
 		current->thread.svcr &= ~SVCR_ZA_MASK;
 		return 0;
 	}
 
 	vq = sve_vq_from_vl(za.vl);
 
-	if (za.head.size < ZA_SIG_CONTEXT_SIZE(vq))
+	if (user->za_size < ZA_SIG_CONTEXT_SIZE(vq))
 		return -EINVAL;
 
 	/*
@@ -521,15 +524,15 @@ static int restore_zt_context(struct user_ctxs *user)
 	if (!thread_za_enabled(&current->thread))
 		return -EINVAL;
 
+	if (user->zt_size != ZT_SIG_CONTEXT_SIZE(1))
+		return -EINVAL;
+
 	if (__copy_from_user(&zt, user->zt, sizeof(zt)))
 		return -EFAULT;
 
 	if (zt.nregs != 1)
 		return -EINVAL;
 
-	if (zt.head.size != ZT_SIG_CONTEXT_SIZE(zt.nregs))
-		return -EINVAL;
-
 	/*
 	 * Careful: we are about __copy_from_user() directly into
 	 * thread.zt_state with preemption enabled, so protection is
@@ -621,6 +624,7 @@ static int parse_user_sigframe(struct user_ctxs *user,
 				goto invalid;
 
 			user->fpsimd = (struct fpsimd_context __user *)head;
+			user->fpsimd_size = size;
 			break;
 
 		case ESR_MAGIC:
@@ -635,6 +639,7 @@ static int parse_user_sigframe(struct user_ctxs *user,
 				goto invalid;
 
 			user->sve = (struct sve_context __user *)head;
+			user->sve_size = size;
 			break;
 
 		case TPIDR2_MAGIC:
@@ -644,10 +649,8 @@ static int parse_user_sigframe(struct user_ctxs *user,
 			if (user->tpidr2)
 				goto invalid;
 
-			if (size != sizeof(*user->tpidr2))
-				goto invalid;
-
 			user->tpidr2 = (struct tpidr2_context __user *)head;
+			user->tpidr2_size = size;
 			break;
 
 		case ZA_MAGIC:
@@ -658,6 +661,7 @@ static int parse_user_sigframe(struct user_ctxs *user,
 				goto invalid;
 
 			user->za = (struct za_context __user *)head;
+			user->za_size = size;
 			break;
 
 		case ZT_MAGIC:
@@ -667,10 +671,8 @@ static int parse_user_sigframe(struct user_ctxs *user,
 			if (user->zt)
 				goto invalid;
 
-			if (size < sizeof(*user->zt))
-				goto invalid;
-
 			user->zt = (struct zt_context __user *)head;
+			user->zt_size = size;
 			break;
 
 		case EXTRA_MAGIC: