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From: Jordan Niethe <jniethe5@gmail.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v2 05/12] powerpc: Do not dereference code as 'struct ppc_inst' (uprobe, code-patching, feature-fixups)
Date: Tue, 15 Jun 2021 13:41:22 +1000	[thread overview]
Message-ID: <CACzsE9qw7CuZdBoSVVUjkcZe6Z8Vzy9iNDVE7E3JLhJER+Z9xw@mail.gmail.com> (raw)
In-Reply-To: <c9a1201dd0a66b4a0f91f0fb46d9385cbf030feb.1621516826.git.christophe.leroy@csgroup.eu>

On Thu, May 20, 2021 at 11:50 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
> 'struct ppc_inst' is an internal structure to represent an instruction,
> it is not directly the representation of that instruction in text code.
> It is not meant to map and dereference code.
>
> Dereferencing code directly through 'struct ppc_inst' has two main issues:
> - On powerpc, structs are expected to be 8 bytes aligned while code is
> spread every 4 byte.
> - Should a non prefixed instruction lie at the end of the page and the
> following page not be mapped, it would generate a page fault.
>
> In-memory code must be accessed with ppc_inst_read().
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/kernel/uprobes.c     | 2 +-
>  arch/powerpc/lib/code-patching.c  | 8 ++++----
>  arch/powerpc/lib/feature-fixups.c | 2 +-
>  3 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> index 186f69b11e94..46971bb41d05 100644
> --- a/arch/powerpc/kernel/uprobes.c
> +++ b/arch/powerpc/kernel/uprobes.c
> @@ -42,7 +42,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
>                 return -EINVAL;
>
>         if (cpu_has_feature(CPU_FTR_ARCH_31) &&
> -           ppc_inst_prefixed(auprobe->insn) &&
> +           ppc_inst_prefixed(ppc_inst_read(&auprobe->insn)) &&
>             (addr & 0x3f) == 60) {
>                 pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
>                 return -EINVAL;
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index 870b30d9be2f..0308429b0d1a 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -329,13 +329,13 @@ static unsigned long branch_iform_target(const struct ppc_inst *instr)
>  {
>         signed long imm;
>
> -       imm = ppc_inst_val(*instr) & 0x3FFFFFC;
> +       imm = ppc_inst_val(ppc_inst_read(instr)) & 0x3FFFFFC;
>
>         /* If the top bit of the immediate value is set this is negative */
>         if (imm & 0x2000000)
>                 imm -= 0x4000000;
>
> -       if ((ppc_inst_val(*instr) & BRANCH_ABSOLUTE) == 0)
> +       if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
>                 imm += (unsigned long)instr;
>
>         return (unsigned long)imm;
> @@ -345,13 +345,13 @@ static unsigned long branch_bform_target(const struct ppc_inst *instr)
>  {
>         signed long imm;
>
> -       imm = ppc_inst_val(*instr) & 0xFFFC;
> +       imm = ppc_inst_val(ppc_inst_read(instr)) & 0xFFFC;
>
>         /* If the top bit of the immediate value is set this is negative */
>         if (imm & 0x8000)
>                 imm -= 0x10000;
>
> -       if ((ppc_inst_val(*instr) & BRANCH_ABSOLUTE) == 0)
> +       if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
>                 imm += (unsigned long)instr;
>
>         return (unsigned long)imm;
> diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
> index fe26f2fa0f3f..8905b53109bc 100644
> --- a/arch/powerpc/lib/feature-fixups.c
> +++ b/arch/powerpc/lib/feature-fixups.c
> @@ -51,7 +51,7 @@ static int patch_alt_instruction(struct ppc_inst *src, struct ppc_inst *dest,
>
>         instr = ppc_inst_read(src);
>
> -       if (instr_is_relative_branch(*src)) {
> +       if (instr_is_relative_branch(ppc_inst_read(src))) {
The above variable instr could be used here, but that is not an issue
with this patch.
>                 struct ppc_inst *target = (struct ppc_inst *)branch_target(src);
>
>                 /* Branch within the section doesn't need translating */
> --
> 2.25.0
>
Reviewed by: Jordan Niethe <jniethe5@gmail.com>

  reply	other threads:[~2021-06-15  3:41 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20 13:50 [PATCH v2 00/12] powerpc: Cleanup use of 'struct ppc_inst' Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 01/12] powerpc/inst: Fix sparse detection on get_user_instr() Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 02/12] powerpc/inst: Reduce casts in get_user_instr() Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 03/12] powerpc/inst: Improve readability of get_user_instr() and friends Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 04/12] powerpc/inst: Avoid pointer dereferencing in ppc_inst_equal() Christophe Leroy
2021-06-15  3:38   ` Jordan Niethe
2021-05-20 13:50 ` [PATCH v2 05/12] powerpc: Do not dereference code as 'struct ppc_inst' (uprobe, code-patching, feature-fixups) Christophe Leroy
2021-06-15  3:41   ` Jordan Niethe [this message]
2021-05-20 13:50 ` [PATCH v2 06/12] powerpc/lib/code-patching: Make instr_is_branch_to_addr() static Christophe Leroy
2021-06-15  3:42   ` Jordan Niethe
2021-05-20 13:50 ` [PATCH v2 07/12] powerpc/lib/code-patching: Don't use struct 'ppc_inst' for runnable code in tests Christophe Leroy
2021-06-15  3:42   ` Jordan Niethe
2021-05-20 13:50 ` [PATCH v2 08/12] powerpc: Don't use 'struct ppc_inst' to reference instruction location Christophe Leroy
2021-06-15  2:01   ` Michael Ellerman
2021-06-15  3:47     ` Jordan Niethe
2021-05-20 13:50 ` [PATCH v2 09/12] powerpc/inst: Refactor PPC32 and PPC64 versions Christophe Leroy
2021-06-15  3:48   ` Jordan Niethe
2021-05-20 13:50 ` [PATCH v2 10/12] powerpc/optprobes: Minimise casts Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 11/12] powerpc/optprobes: Compact code source a bit Christophe Leroy
2021-05-20 13:50 ` [PATCH v2 12/12] powerpc/optprobes: use PPC_RAW_ macros Christophe Leroy
2021-06-08 12:46 ` [PATCH v2 00/12] powerpc: Cleanup use of 'struct ppc_inst' Christophe Leroy
2021-06-15  7:18 ` Michael Ellerman
2021-06-15  7:24   ` Christophe Leroy
2021-06-16 13:05     ` Michael Ellerman
2021-06-18  3:51 ` Michael Ellerman

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