From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Jessica Yu <jeyu@kernel.org>
Subject: Re: [PATCH v2 2/9] livepatch: Apply vmlinux-specific KLP relocations early
Date: Mon, 20 Apr 2020 13:25:16 -0500 [thread overview]
Message-ID: <20200420182516.6awwwbvoen62gwbr@treble> (raw)
In-Reply-To: <20200420175751.GA13807@redhat.com>
On Mon, Apr 20, 2020 at 01:57:51PM -0400, Joe Lawrence wrote:
> On Fri, Apr 17, 2020 at 09:04:27AM -0500, Josh Poimboeuf wrote:
> >
> > [ ... snip ... ]
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 40cfac8156fd..5fda3afc0285 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> >
> > [ ... snip ... ]
> >
> > +int klp_write_relocations(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> > + const char *shstrtab, const char *strtab,
> > + unsigned int symndx, struct module *pmod,
> > + const char *objname)
> > {
> > int i, cnt, ret = 0;
> > - const char *objname, *secname;
> > char sec_objname[MODULE_NAME_LEN];
> > Elf_Shdr *sec;
> >
> > - if (WARN_ON(!klp_is_object_loaded(obj)))
> > - return -EINVAL;
> > -
> > - objname = klp_is_module(obj) ? obj->name : "vmlinux";
> > -
> > /* For each klp relocation section */
> > - for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> > - sec = pmod->klp_info->sechdrs + i;
> > - secname = pmod->klp_info->secstrings + sec->sh_name;
> > + for (i = 1; i < ehdr->e_shnum; i++) {
> > + sec = sechdrs + i;
>
> Hi Josh, minor bug:
>
> Note the for loop through the section headers in
> klp_write_relocations(), but its calling function ...
>
> > [ ... snip ... ]
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 646f1e2330d2..d36ea8a8c3ec 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -2334,11 +2334,12 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
> > if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
> > continue;
> >
> > - /* Livepatch relocation sections are applied by livepatch */
> > if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
> > - continue;
> > -
> > - if (info->sechdrs[i].sh_type == SHT_REL)
> > + err = klp_write_relocations(info->hdr, info->sechdrs,
> > + info->secstrings,
> > + info->strtab,
> > + info->index.sym, mod, NULL);
> > + else if (info->sechdrs[i].sh_type == SHT_REL)
> > err = apply_relocate(info->sechdrs, info->strtab,
> > info->index.sym, i, mod);
> > else if (info->sechdrs[i].sh_type == SHT_RELA)
>
> ... apply_relocations() is also iterating over the section headers (the
> diff context doesn't show it here, but i is an incrementing index over
> sechdrs[]).
>
> So if there is more than one KLP relocation section, we'll process them
> multiple times. At least the x86 relocation code will detect this and
> fail the module load with an invalid relocation (existing value not
> zero).
Ah, yes, good catch!
--
Josh
next prev parent reply other threads:[~2020-04-20 18:25 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 14:04 [PATCH v2 0/9] livepatch,module: Remove .klp.arch and module_disable_ro() Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 1/9] livepatch: Disallow vmlinux.ko Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 2/9] livepatch: Apply vmlinux-specific KLP relocations early Josh Poimboeuf
2020-04-20 17:57 ` Joe Lawrence
2020-04-20 18:25 ` Josh Poimboeuf [this message]
2020-04-20 19:01 ` Joe Lawrence
2020-04-20 19:11 ` Josh Poimboeuf
2020-04-20 19:49 ` Joe Lawrence
2020-04-20 19:51 ` Josh Poimboeuf
2020-04-23 1:10 ` Joe Lawrence
2020-04-21 11:54 ` Miroslav Benes
2020-04-17 14:04 ` [PATCH v2 3/9] livepatch: Remove .klp.arch Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 4/9] livepatch: Prevent module-specific KLP rela sections from referencing vmlinux symbols Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 5/9] s390: Change s390_kernel_write() return type to match memcpy() Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations Josh Poimboeuf
2020-04-22 12:28 ` Miroslav Benes
2020-04-24 13:43 ` Josh Poimboeuf
2020-04-22 14:40 ` Gerald Schaefer
2020-04-22 15:21 ` Gerald Schaefer
2020-04-22 19:46 ` Josh Poimboeuf
2020-04-23 12:33 ` Gerald Schaefer
2020-04-23 13:22 ` Miroslav Benes
2020-04-23 14:12 ` Josh Poimboeuf
2020-04-23 18:10 ` Josh Poimboeuf
2020-04-23 23:26 ` Josh Poimboeuf
2020-04-24 2:35 ` Joe Lawrence
2020-04-24 4:12 ` Josh Poimboeuf
2020-04-24 7:20 ` Christian Borntraeger
2020-04-24 13:37 ` Josh Poimboeuf
2020-04-30 14:38 ` Joe Lawrence
2020-04-30 16:48 ` Josh Poimboeuf
2020-04-30 17:04 ` Joe Lawrence
2020-04-23 14:21 ` Joe Lawrence
2020-04-17 14:04 ` [PATCH v2 7/9] x86/module: Use text_poke() " Josh Poimboeuf
2020-04-17 14:29 ` Peter Zijlstra
2020-04-17 14:51 ` Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 8/9] livepatch: Remove module_disable_ro() usage Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 9/9] module: Remove module_disable_ro() Josh Poimboeuf
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