From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Keir Fraser <keir@xen.org>,
ross.lagerwall@citrix.com, andrew.cooper3@citrix.com,
mpohlack@amazon.de, Julien Grall <julien.grall@arm.com>,
sasha.levin@oracle.com, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v9 11/27] xsplice: Implement payload loading
Date: Tue, 26 Apr 2016 21:47:00 -0400 [thread overview]
Message-ID: <20160427014654.GA26540@localhost.localdomain> (raw)
In-Reply-To: <571F8B9F02000078000E5E09@prv-mh.provo.novell.com>
> > +static int move_payload(struct payload *payload, struct xsplice_elf *elf)
> > +{
.. snip..
> > + /* Compute size of different regions. */
> > + for ( i = 1; i < elf->hdr->e_shnum; i++ )
> > + {
> > + if ( (elf->sec[i].sec->sh_flags & (SHF_ALLOC|SHF_EXECINSTR)) ==
> > + (SHF_ALLOC|SHF_EXECINSTR) )
> > + calc_section(&elf->sec[i], &payload->text_size, &offset[i]);
>
> This silently accepts writable text sections, yet the portion of the
> memory this gets placed in will be mapped RX.
I am not sure I follow. We only accept if sh_flags have AX. Not WAX?
How am I accepting writable text sections?
>
> > + else if ( (elf->sec[i].sec->sh_flags & SHF_ALLOC) &&
> > + !(elf->sec[i].sec->sh_flags & SHF_EXECINSTR) &&
> > + (elf->sec[i].sec->sh_flags & SHF_WRITE) )
> > + calc_section(&elf->sec[i], &payload->rw_size, &offset[i]);
> > + else if ( (elf->sec[i].sec->sh_flags & SHF_ALLOC) &&
> > + !(elf->sec[i].sec->sh_flags & SHF_EXECINSTR) &&
> > + !(elf->sec[i].sec->sh_flags & SHF_WRITE) )
> > + calc_section(&elf->sec[i], &payload->ro_size, &offset[i]);
> > + else if ( !elf->sec[i].sec->sh_flags ||
> > + (elf->sec[i].sec->sh_flags & SHF_EXECINSTR) ||
> > + (elf->sec[i].sec->sh_flags & SHF_MASKPROC) )
> > + /* Do nothing.*/;
> > + else if ( (elf->sec[i].sec->sh_flags & SHF_ALLOC) &&
> > + (elf->sec[i].sec->sh_type == SHT_NOBITS) )
> > + {
> > + dprintk(XENLOG_DEBUG, XSPLICE "%s: Not supporting %s section!\n",
> > + elf->name, elf->sec[i].name);
> > + rc = -EOPNOTSUPP;
> > + goto out;
> > + }
>
> I saw this in the changelog, but I don't really understand these last
> two conditionals. Wouldn't you want to bail on _any_ sections which
The first (/Do nothing/) is for sections such as .rela.* (which we can
ditch after we are done), .symtab, .strtab (for which in later patches in
build_symbol_table construct a copy), and:
[ 1] .note.gnu.build-i NOTE 0000000000000000 00000040
0000000000000024 0000000000000000 A 0 0 4
which value we just copy in struct payload->id.
(also in later patch).
> have SHF_ALLOC set but don't get mapped to one of the three
> blocks? And wouldn't you (silently) ignore any sections with SHF_ALLOC
> clear?
Correct, such as:
[29] .shstrtab STRTAB 0000000000000000 000002fe
0000000000000143 0000000000000000 0 0 1
I've update the comments to be more clear.
..snip..
> > +int xsplice_elf_resolve_symbols(struct xsplice_elf *elf)
> > +{
> > + unsigned int i;
> > + int rc = 0;
> > +
> > + ASSERT(elf->sym);
> > +
> > + for ( i = 1; i < elf->nsym; i++ )
> > + {
> > + unsigned int idx = elf->sym[i].sym->st_shndx;
> > + Elf_Sym *sym = (Elf_Sym *)elf->sym[i].sym;
>
> Well, I admit that this is the more straightforward solution, but it
> opens up all of what sym points to for writing. I.e. I'd have
> considered it much better to really only do the casting away of
> const in the one spot where you need it (see below).
OK. That may become a bit cumbersome. We would have in the later
patches (xsplice,symbols: Implement symbol name resolution on addres)
the SHN_UNDEF doing symbol lookup. And that one tries to set
sym->st_value twice.
I can certainly cast it twice there, and then once in the default
case if you would like.
>
> > + switch ( idx )
> > + {
> > + case SHN_COMMON:
> > + dprintk(XENLOG_ERR, XSPLICE "%s: Unexpected common symbol: %s\n",
> > + elf->name, elf->sym[i].name);
> > + rc = -EINVAL;
> > + break;
> > +
> > + case SHN_UNDEF:
> > + dprintk(XENLOG_ERR, XSPLICE "%s: Unknown symbol: %s\n",
> > + elf->name, elf->sym[i].name);
> > + rc = -ENOENT;
> > + break;
..snip..
> > + default:
..snip..
> > +
> > + sym->st_value += (unsigned long)elf->sec[idx].load_addr;
>
> *(<type> *)&sym->st_value += ...
Right, so I can cast it to a non-const and write to it. Keep in mind
that in this patch it is only one place, but in further I would have
to do this twice.
What is your preference?
>
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next prev parent reply other threads:[~2016-04-27 1:47 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 15:34 [PATCH 9] xSplice v1 design and implementation Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 01/27] Revert "libxc/libxl/python/xenstat/ocaml: Use new XEN_VERSION hypercall" Konrad Rzeszutek Wilk
2016-04-25 15:48 ` Jan Beulich
2016-04-25 15:53 ` Wei Liu
2016-04-25 15:34 ` [PATCH v9 02/27] Revert "HYPERCALL_version_op. New hypercall mirroring XENVER_ but sane." Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 03/27] xsplice: Design document Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 04/27] xen/xsplice: Hypervisor implementation of XEN_XSPLICE_op Konrad Rzeszutek Wilk
2016-04-26 7:48 ` Ross Lagerwall
2016-04-26 7:52 ` Ross Lagerwall
2016-04-26 10:21 ` Jan Beulich
2016-04-26 17:50 ` Konrad Rzeszutek Wilk
2016-04-27 6:51 ` Jan Beulich
2016-04-27 13:47 ` Konrad Rzeszutek Wilk
2016-04-27 14:11 ` Jan Beulich
2016-04-25 15:34 ` [PATCH v9 05/27] libxc: Implementation of XEN_XSPLICE_op in libxc Konrad Rzeszutek Wilk
2016-04-26 7:51 ` Ross Lagerwall
2016-04-25 15:34 ` [PATCH v9 06/27] xen-xsplice: Tool to manipulate xsplice payloads Konrad Rzeszutek Wilk
2016-04-26 7:49 ` Ross Lagerwall
2016-04-25 15:34 ` [PATCH v9 07/27] arm/x86: Use struct virtual_region to do bug, symbol, and (x86) exception tables lookup Konrad Rzeszutek Wilk
2016-04-26 10:31 ` Jan Beulich
2016-04-25 15:34 ` [PATCH v9 08/27] arm/x86/vmap: Add v[z|m]alloc_xen and vm_init_type Konrad Rzeszutek Wilk
2016-04-26 10:47 ` Jan Beulich
2016-04-27 2:38 ` Konrad Rzeszutek Wilk
2016-04-27 7:12 ` Jan Beulich
2016-04-27 13:46 ` Konrad Rzeszutek Wilk
2016-04-27 14:15 ` Jan Beulich
2016-04-25 15:34 ` [PATCH v9 09/27] x86/mm: Introduce modify_xen_mappings() Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 10/27] xsplice: Add helper elf routines Konrad Rzeszutek Wilk
2016-04-26 10:05 ` Ross Lagerwall
2016-04-26 11:52 ` Jan Beulich
2016-04-26 12:37 ` Jan Beulich
2016-04-27 1:59 ` Konrad Rzeszutek Wilk
2016-04-27 7:27 ` Jan Beulich
2016-04-27 14:00 ` Konrad Rzeszutek Wilk
2016-04-27 4:06 ` Konrad Rzeszutek Wilk
2016-04-27 7:52 ` Jan Beulich
2016-04-27 18:45 ` Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 11/27] xsplice: Implement payload loading Konrad Rzeszutek Wilk
2016-04-26 10:48 ` Ross Lagerwall
2016-04-26 13:39 ` Jan Beulich
2016-04-27 1:47 ` Konrad Rzeszutek Wilk [this message]
2016-04-27 7:57 ` Jan Beulich
2016-04-27 3:28 ` Konrad Rzeszutek Wilk
2016-04-27 8:28 ` Jan Beulich
2016-04-27 15:48 ` Konrad Rzeszutek Wilk
2016-04-27 16:06 ` Jan Beulich
2016-04-27 16:14 ` Jan Beulich
2016-04-27 18:40 ` Konrad Rzeszutek Wilk
2016-04-25 15:34 ` [PATCH v9 12/27] xsplice: Implement support for applying/reverting/replacing patches Konrad Rzeszutek Wilk
2016-04-26 15:21 ` Jan Beulich
2016-04-27 3:39 ` Konrad Rzeszutek Wilk
2016-04-27 8:36 ` Jan Beulich
2016-05-11 9:51 ` Martin Pohlack
2016-05-11 13:56 ` Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 13/27] x86/xen_hello_world.xsplice: Test payload for patching 'xen_extra_version' Konrad Rzeszutek Wilk
2016-04-26 15:31 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 14/27] xsplice, symbols: Implement symbol name resolution on address Konrad Rzeszutek Wilk
2016-04-26 15:48 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 15/27] xsplice, symbols: Implement fast symbol names -> virtual addresses lookup Konrad Rzeszutek Wilk
2016-04-26 15:53 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 16/27] x86, xsplice: Print payload's symbol name and payload name in backtraces Konrad Rzeszutek Wilk
2016-04-26 11:06 ` Ross Lagerwall
2016-04-26 12:41 ` Jan Beulich
2016-04-26 12:48 ` Ross Lagerwall
2016-04-26 13:41 ` Jan Beulich
2016-04-27 3:31 ` Konrad Rzeszutek Wilk
2016-04-27 8:37 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 17/27] xsplice: Add support for bug frames Konrad Rzeszutek Wilk
2016-04-26 11:05 ` Ross Lagerwall
2016-04-26 13:08 ` Ross Lagerwall
2016-04-26 15:58 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 18/27] xsplice: Add support for exception tables Konrad Rzeszutek Wilk
2016-04-26 16:01 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 19/27] xsplice: Add support for alternatives Konrad Rzeszutek Wilk
2016-04-27 8:58 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 20/27] build_id: Provide ld-embedded build-ids Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 21/27] xsplice: Print build_id in keyhandler and on bootup Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 22/27] XENVER_build_id/libxc: Provide ld-embedded build-id Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 23/27] libxl: info: Display build_id of the hypervisor Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 24/27] xsplice: Stacking build-id dependency checking Konrad Rzeszutek Wilk
2016-04-27 9:27 ` Jan Beulich
2016-04-27 16:36 ` Konrad Rzeszutek Wilk
2016-04-28 9:47 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 25/27] xsplice/xen_replace_world: Test-case for XSPLICE_ACTION_REPLACE Konrad Rzeszutek Wilk
2016-04-25 15:35 ` [PATCH v9 26/27] xsplice: Prevent duplicate payloads from being loaded Konrad Rzeszutek Wilk
2016-04-27 9:31 ` Jan Beulich
2016-04-25 15:35 ` [PATCH v9 27/27] MAINTAINERS/xsplice: Add myself and Ross as the maintainers Konrad Rzeszutek Wilk
2016-04-25 15:41 ` [PATCH 9] xSplice v1 design and implementation Jan Beulich
2016-04-25 15:47 ` Konrad Rzeszutek Wilk
2016-04-25 15:54 ` Jan Beulich
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