arm64: BTI: Decode BYTPE bits when printing PSTATE

The current code to print PSTATE symbolically when generating
backtraces etc., does not include the BYTPE field used by Branch
Target Identification.

So, decode BYTPE and print it too.

In the interests of human-readability, print the classes of BTI
matched.  The symbolic notation, BYTPE (PSTATE[11:10]) and
permitted classes of subsequent instruction are:

    -- (BTYPE=0b00): any insn
    jc (BTYPE=0b01): BTI jc, BTI j, BTI c, PACIxSP
    -c (BYTPE=0b10): BTI jc, BTI c, PACIxSP
    j- (BTYPE=0b11): BTI jc, BTI j
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/process.c

@@ -211,6 +211,15 @@ void machine_restart(char *cmd)
 	while (1);
 }
 
+#define bstr(suffix, str) [PSR_BTYPE_ ## suffix >> PSR_BTYPE_SHIFT] = str
+static const char *const btypes[] = {
+	bstr(NONE, "--"),
+	bstr(  JC, "jc"),
+	bstr(   C, "-c"),
+	bstr(  J , "j-")
+};
+#undef bstr
+
 static void print_pstate(struct pt_regs *regs)
 {
 	u64 pstate = regs->pstate;
@@ -229,7 +238,10 @@ static void print_pstate(struct pt_regs *regs)
 			pstate & PSR_AA32_I_BIT ? 'I' : 'i',
 			pstate & PSR_AA32_F_BIT ? 'F' : 'f');
 	} else {
-		printk("pstate: %08llx (%c%c%c%c %c%c%c%c %cPAN %cUAO)\n",
+		const char *btype_str = btypes[(pstate & PSR_BTYPE_MASK) >>
+					       PSR_BTYPE_SHIFT];
+
+		printk("pstate: %08llx (%c%c%c%c %c%c%c%c %cPAN %cUAO BTYPE=%s)\n",
 			pstate,
 			pstate & PSR_N_BIT ? 'N' : 'n',
 			pstate & PSR_Z_BIT ? 'Z' : 'z',
@@ -240,7 +252,8 @@ static void print_pstate(struct pt_regs *regs)
 			pstate & PSR_I_BIT ? 'I' : 'i',
 			pstate & PSR_F_BIT ? 'F' : 'f',
 			pstate & PSR_PAN_BIT ? '+' : '-',
-			pstate & PSR_UAO_BIT ? '+' : '-');
+			pstate & PSR_UAO_BIT ? '+' : '-',
+			btype_str);
 	}
 }