linux-kernel - [PATCH v3 08/12] arm64: BTI: Decode BYTPE bits when printing PSTATE

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Date:   Fri, 18 Oct 2019 18:25:41 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Jones <drjones@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Sudakshina Das <sudi.das@....com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v3 08/12] 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: Dave Martin <Dave.Martin@....com>

---

Changes since v2:

 * Split out the PSR_BYTPE_* definitions that for merging into
   "arm64: Basic Branch Target Identification support".
---
 arch/arm64/kernel/process.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 4c78937..a2b555a 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -209,6 +209,15 @@ 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;
@@ -227,7 +236,10 @@ 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',
@@ -238,7 +250,8 @@ 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);
 	}
 }
 
-- 
2.1.4