[PATCH 14/17] MIPS: bpf: Prevent kernel fall over for >=32bit shifts

Remove BUG_ON() if the shift immediate is >=32 to avoid
kernel crashes due to malicious user input. Since the micro-assembler
will not allow an immediate greater or equal to 32, we will use the
maximum value which is 31. This will do the correct thing on either 32-
or 64-bit cores since no 64-bit instructions are being used in JIT.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Daniel Borkmann <redacted>
Cc: Alexei Starovoitov <redacted>
Cc: netdev@vger.kernel.org
Signed-off-by: Markos Chandras <redacted>
---
 arch/mips/net/bpf_jit.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 1bcd599d9971..09ebc886c7aa 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c

@@ -309,7 +309,8 @@ static inline void emit_sll(unsigned int dst, unsigned int src,
 			    unsigned int sa, struct jit_ctx *ctx)
 {
 	/* sa is 5-bits long */
-	BUG_ON(sa >= BIT(5));
+	if (sa >= BIT(5))
+		sa = BIT(5) - 1;
 	emit_instr(ctx, sll, dst, src, sa);
 }
 

@@ -323,7 +324,8 @@ static inline void emit_srl(unsigned int dst, unsigned int src,
 			    unsigned int sa, struct jit_ctx *ctx)
 {
 	/* sa is 5-bits long */
-	BUG_ON(sa >= BIT(5));
+	if (sa >= BIT(5))
+		sa =  BIT(5) - 1;
 	emit_instr(ctx, srl, dst, src, sa);
 }
 

-- 
2.0.0