riscv: cpu: improve multi-letter extension detection in supports_extension()

The first multi-letter extension after the single-letter extensions does
not have to be preceded by an underscore, which could cause the parser
to mistakenly find a single-letter extension after the start of the
multi-letter portion of the string.
Three letters precede multi-letter extensions (s, x & z), none of which
are valid single-letter extensions. The dt-binding also allows
multi-letter extensions starting with h, but no such extension have been
frozen or ratified, and the unprivileged spec no longer uses "h" as a
prefix for multi-letter hypervisor extensions, having moved to "sh"
instead. For that reason, modify the parser to stop at s, x & z to prevent
this overrun, ignoring h.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

1 files changed, 16 insertions, 6 deletions

diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index 8445c58..ecfefa1 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -49,14 +49,24 @@ static inline bool supports_extension(char ext)
 	}
 	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
 		/*
-		 * skip the first 4 characters (rv32|rv64) and
-		 * check until underscore
+		 * skip the first 4 characters (rv32|rv64)
 		 */
 		for (i = 4; i < sizeof(desc); i++) {
-			if (desc[i] == '_' || desc[i] == '\0')
-				break;
-			if (desc[i] == ext)
-				return true;
+			switch (desc[i]) {
+			case 's':
+			case 'x':
+			case 'z':
+			case '_':
+			case '\0':
+				/*
+				 * Any of these characters mean the single
+				 * letter extensions have all been consumed.
+				 */
+				return false;
+			default:
+				if (desc[i] == ext)
+					return true;
+			}
 		}
 	}