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Message-ID: <CAJF2gTTdEY-H7QrVyY31Z5nCG0yqo4Zo9W1dBbGEzRqZdec55Q@mail.gmail.com>
Date: Tue, 29 Aug 2023 17:48:19 +0800
From: Guo Ren <guoren@...nel.org>
To: Nam Cao <namcaov@...il.com>
Cc: 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, conor.dooley@...rochip.com,
Björn Töpel <bjorn@...osinc.com>
Subject: Re: [PATCH v2] riscv: provide riscv-specific is_trap_insn()
Thx for the fix.
Reviewed-by: Guo Ren <guoren@...nel.org>
On Tue, Aug 29, 2023 at 4:37 PM Nam Cao <namcaov@...il.com> wrote:
>
> 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 causes an infinite loop of entering
> and exiting trap handler.
>
> Instead of using the default implementation, implement this function
> speficially for riscv with checks for both ebreak and c.ebreak.
>
> Fixes: 74784081aac8 ("riscv: Add uprobes supported")
> Signed-off-by: Nam Cao <namcaov@...il.com>
> Tested-by: Björn Töpel <bjorn@...osinc.com>
> ---
> v2: remove #ifdef CONFIG_RISCV_ISA_C (Guo Ren)
>
> arch/riscv/kernel/probes/uprobes.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/riscv/kernel/probes/uprobes.c b/arch/riscv/kernel/probes/uprobes.c
> index 194f166b2cc4..4b3dc8beaf77 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 +18,11 @@ bool is_swbp_insn(uprobe_opcode_t *insn)
> #endif
> }
>
> +bool is_trap_insn(uprobe_opcode_t *insn)
> +{
> + return riscv_insn_is_ebreak(*insn) || riscv_insn_is_c_ebreak(*insn);
> +}
> +
> unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
> {
> return instruction_pointer(regs);
> --
> 2.34.1
>
--
Best Regards
Guo Ren
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