[RESEND PATCH v4 7/8] arm64: Forbid calling compat sigreturn from 64-bit tasks

[Amanieu d'Antras]

It's impossible for this syscall to do anything sensible in this
context.

Signed-off-by: Amanieu d'Antras <amanieu@xxxxxxxxx>
Co-developed-by: Ryan Houdek <Houdek.Ryan@xxxxxxxxxxx>
Signed-off-by: Ryan Houdek <Houdek.Ryan@xxxxxxxxxxx>
---
 arch/arm64/kernel/signal32.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index 2f507f565c48..e2bdd1eaefd8 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -237,6 +237,10 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
 
+	/* Reject attempts to call this from a 64-bit process. */
+	if (!is_compat_task())
+		goto badframe;
+
 	/*
 	 * Since we stacked the signal on a 64-bit boundary,
 	 * then 'sp' should be word aligned here.  If it's
@@ -268,6 +272,10 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
 
+	/* Reject attempts to call this from a 64-bit process. */
+	if (!is_compat_task())
+		goto badframe;
+
 	/*
 	 * Since we stacked the signal on a 64-bit boundary,
 	 * then 'sp' should be word aligned here.  If it's
-- 
2.31.1