MIPS: BPF: Fix stack pointer allocation

Fix stack pointer offset which could potentially corrupt
argument registers in the previous frame. The calculated offset
reflects the size of all the registers we need to preserve so there
is no need for this erroneous subtraction.

[[email protected]: Fixed conflict due to only applying this fix part
of the entire series as part of 4.1 fixes.]

Signed-off-by: Markos Chandras <[email protected]>
Cc: [email protected]
Cc: "David S. Miller" <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Hannes Frederic Sowa <[email protected]>
Cc: [email protected]
Cc: [email protected]
Patchwork: http://patchwork.linux-mips.org/patch/10527/
Signed-off-by: Ralf Baechle <[email protected]>

Author: Markos Chandras

arch/mips/net/bpf_jit.c

@@ -681,11 +681,7 @@ static unsigned int get_stack_depth(struct jit_ctx *ctx)
 		sp_off += config_enabled(CONFIG_64BIT) ?
 			(ARGS_USED_BY_JIT + 1) * RSIZE : RSIZE;
 
-	/*
-	 * Subtract the bytes for the last registers since we only care about
-	 * the location on the stack pointer.
-	 */
-	return sp_off - RSIZE;
+	return sp_off;
 }
 
 static void build_prologue(struct jit_ctx *ctx)