From: "Jan Beulich" <JBeulich@suse.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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: Wed, 27 Apr 2016 01:57:32 -0600 [thread overview]
Message-ID: <57208D0C02000078000E630A@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160427014654.GA26540@localhost.localdomain>
>>> On 27.04.16 at 03:47, <konrad.wilk@oracle.com> wrote:
>> > +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?
Because the & masks off SHF_WRITE, i.e. you only check that
SHF_ALLOC and SHF_EXECINSTR are set, but not that SHF_WRITE
is clear.
>> > + 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).
All of which would fall under the "ignore sections with SHF_ALLOC
clear" rule, as mentioned ...
>> 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?
... here.
>> > +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.
How about calculating the new value into a local variable, and doing
the cast needed for the assignment just once after the switch()?
Jan
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next prev parent reply other threads:[~2016-04-27 7:57 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
2016-04-27 7:57 ` Jan Beulich [this message]
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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