linux-kernel - [PATCH 8/8] arm64: BTI: Decode BYTPE bits when printing PSTATE

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Date:   Fri, 24 May 2019 11:25:33 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Richard Henderson <richard.henderson@...aro.org>,
        Andrew Jones <drjones@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Sudakshina Das <sudi.das@....com>,
        Paul Elliott <paul.elliott@....com>
Subject: [PATCH 8/8] 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 motation, 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>
---
 arch/arm64/include/asm/ptrace.h | 4 +++-
 arch/arm64/kernel/process.c     | 9 +++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index b868ef11..f91e51c 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -40,8 +40,10 @@
 #define GIC_PRIO_IRQOFF		(GIC_PRIO_IRQON & ~0x80)
 
 /* Additional SPSR bits not exposed in the UABI */
+#define PSR_BTYPE_SHIFT		10
+
 #define PSR_IL_BIT		(1 << 20)
-#define PSR_BTYPE_CALL		(2 << 10)
+#define PSR_BTYPE_CALL		(2 << PSR_BTYPE_SHIFT)
 
 /* AArch32-specific ptrace requests */
 #define COMPAT_PTRACE_GETREGS		12
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 104b0d8..dde5c40 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -236,7 +236,11 @@ 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",
+		static const char *const btypes[] = { "--", "jc", "-c", "j-" };
+		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',
@@ -247,7 +251,8 @@ 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