linux-kernel - [PATCH] riscv: provide riscv-specific is_trap

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Message-Id: <20230827205641.46836-1-namcaov@gmail.com>
Date:   Sun, 27 Aug 2023 22:56:41 +0200
From:   Nam Cao <namcaov@...il.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bjorn@...nel.org, guoren@...nel.org
Cc:     Nam Cao <namcaov@...il.com>
Subject: [PATCH] riscv: provide riscv-specific is_trap_insn()

uprobes expects is_trap_insn() to return true for any trap instructions,
not just the one used for installing uprobe. The current default
implementation only returns true for 16-bit c.ebreak if C extension is
enabled. This can confuse uprobes if a 32-bit ebreak generates a trap
exception from userspace: uprobes asks is_trap_insn() who says there is no
trap, so uprobes assume a probe was there before but has been removed, and
return to the trap instruction. This cause an infinite loop of entering
and exiting trap handler.

Instead of using the default implementation, implement this function
speficially for riscv which checks for both ebreak and c.ebreak.

Fixes: 74784081aac8 ("riscv: Add uprobes supported")
Signed-off-by: Nam Cao <namcaov@...il.com>
---
 arch/riscv/kernel/probes/uprobes.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/riscv/kernel/probes/uprobes.c b/arch/riscv/kernel/probes/uprobes.c
index 194f166b2cc4..91f4ce101cd1 100644
--- a/arch/riscv/kernel/probes/uprobes.c
+++ b/arch/riscv/kernel/probes/uprobes.c
@@ -3,6 +3,7 @@
 #include <linux/highmem.h>
 #include <linux/ptrace.h>
 #include <linux/uprobes.h>
+#include <asm/insn.h>

 #include "decode-insn.h"

@@ -17,6 +18,15 @@ bool is_swbp_insn(uprobe_opcode_t *insn)
 #endif
 }

+bool is_trap_insn(uprobe_opcode_t *insn)
+{
+#ifdef CONFIG_RISCV_ISA_C
+	if (riscv_insn_is_c_ebreak(*insn))
+		return true;
+#endif
+	return riscv_insn_is_ebreak(*insn);
+}
+
 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
 {
 	return instruction_pointer(regs);
-- 
2.34.1