[PATCH 5.17 0120/1126] arm64: signal: nofpsimd: Do not allocate fp/simd context when not available

[Greg Kroah-Hartman]

From: David Engraf <david.engraf@xxxxxxxxx>

commit 0a32c88ddb9af30e8a16d41d7b9b824c27d29459 upstream.

Commit 6d502b6ba1b2 ("arm64: signal: nofpsimd: Handle fp/simd context for
signal frames") introduced saving the fp/simd context for signal handling
only when support is available. But setup_sigframe_layout() always
reserves memory for fp/simd context. The additional memory is not touched
because preserve_fpsimd_context() is not called and thus the magic is
invalid.

This may lead to an error when parse_user_sigframe() checks the fp/simd
area and does not find a valid magic number.

Signed-off-by: David Engraf <david.engraf@xxxxxxxxx>
Reviwed-by: Mark Brown <broonie@xxxxxxxxxx>
Fixes: 6d502b6ba1b267b3 ("arm64: signal: nofpsimd: Handle fp/simd context for signal frames")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.6.x
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Link: https://lore.kernel.org/r/20220225104008.820289-1-david.engraf@xxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/signal.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -577,10 +577,12 @@ static int setup_sigframe_layout(struct
 {
 	int err;
 
-	err = sigframe_alloc(user, &user->fpsimd_offset,
-			     sizeof(struct fpsimd_context));
-	if (err)
-		return err;
+	if (system_supports_fpsimd()) {
+		err = sigframe_alloc(user, &user->fpsimd_offset,
+				     sizeof(struct fpsimd_context));
+		if (err)
+			return err;
+	}
 
 	/* fault information, if valid */
 	if (add_all || current->thread.fault_code) {