linux-kernel - Re: [PATCH v2 04/12] powerpc/inst: Avoid pointer dereferencing in ppc_inst

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Date:   Tue, 15 Jun 2021 13:38:06 +1000
From:   Jordan Niethe <jniethe5@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 04/12] powerpc/inst: Avoid pointer dereferencing in ppc_inst_equal()

On Thu, May 20, 2021 at 11:50 PM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
> Avoid casting/dereferencing ppc_inst() as u64* , check each member
> of the struct when relevant.
>
> And remove the 0xff initialisation of the suffix for non
> prefixed instruction. An instruction with 0xff as a suffix
> might be invalid, but still is a prefixed instruction and
> has to be considered as this.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/inst.h | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm/inst.h
> index fc6adef528a5..5a0740ebf132 100644
> --- a/arch/powerpc/include/asm/inst.h
> +++ b/arch/powerpc/include/asm/inst.h
> @@ -61,7 +61,7 @@ static inline int ppc_inst_primary_opcode(struct ppc_inst x)
>  }
>
>  #ifdef CONFIG_PPC64
> -#define ppc_inst(x) ((struct ppc_inst){ .val = (x), .suffix = 0xff })
> +#define ppc_inst(x) ((struct ppc_inst){ .val = (x) })
>
>  #define ppc_inst_prefix(x, y) ((struct ppc_inst){ .val = (x), .suffix = (y) })
>
> @@ -72,7 +72,7 @@ static inline u32 ppc_inst_suffix(struct ppc_inst x)
>
>  static inline bool ppc_inst_prefixed(struct ppc_inst x)
>  {
> -       return ppc_inst_primary_opcode(x) == OP_PREFIX && ppc_inst_suffix(x) != 0xff;
> +       return ppc_inst_primary_opcode(x) == OP_PREFIX;
>  }
>
>  static inline struct ppc_inst ppc_inst_swab(struct ppc_inst x)
> @@ -93,11 +93,6 @@ static inline struct ppc_inst ppc_inst_read(const struct ppc_inst *ptr)
>         }
>  }
>
> -static inline bool ppc_inst_equal(struct ppc_inst x, struct ppc_inst y)
> -{
> -       return *(u64 *)&x == *(u64 *)&y;
> -}
> -
>  #else
>
>  #define ppc_inst(x) ((struct ppc_inst){ .val = x })
> @@ -124,13 +119,17 @@ static inline struct ppc_inst ppc_inst_read(const struct ppc_inst *ptr)
>         return *ptr;
>  }
>
> +#endif /* CONFIG_PPC64 */
> +
>  static inline bool ppc_inst_equal(struct ppc_inst x, struct ppc_inst y)
>  {
> -       return ppc_inst_val(x) == ppc_inst_val(y);
> +       if (ppc_inst_val(x) != ppc_inst_val(y))
> +               return false;
> +       if (!ppc_inst_prefixed(x))
> +               return true;
> +       return ppc_inst_suffix(x) == ppc_inst_suffix(y);
>  }
>
> -#endif /* CONFIG_PPC64 */
> -
>  static inline int ppc_inst_len(struct ppc_inst x)
>  {
>         return ppc_inst_prefixed(x) ? 8 : 4;
> --
> 2.25.0
>
Reviewed by: Jordan Niethe <jniethe5@...il.com>