linux-kernel - [PATCH] arm64: signal: nofpsimd: Do not allocate fp/simd context when not available

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Date:   Fri, 25 Feb 2022 11:40:08 +0100
From:   David Engraf <david.engraf@...go.com>
To:     suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        broonie@...nel.org, mark.rutland@....com, elver@...gle.com,
        ebiederm@...ssion.com, seanjc@...gle.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Engraf <david.engraf@...go.com>
Subject: [PATCH] arm64: signal: nofpsimd: Do not allocate fp/simd context when not available

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@...go.com>
---
 arch/arm64/kernel/signal.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index d8aaf4b6f432..3d66fba69016 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -577,10 +577,12 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
 {
 	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) {
-- 
2.25.1