linux-kernel - Re: [patch 1/2] Relocate VDSO ELF headers to match mapped location with COMPAT

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Date:	Thu, 05 Apr 2007 08:10:40 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	<virtualization@...ts.osdl.org>,
	"Roland McGrath" <roland@...hat.com>, "Andi Kleen" <ak@...e.de>,
	"lkml" <linux-kernel@...r.kernel.org>,
	"Zachary Amsden" <zach@...are.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [patch 1/2] Relocate VDSO ELF headers to match mapped
	location with COMPAT_VDSO

>+static __cpuinit void reloc_dyn(Elf32_Ehdr *ehdr, unsigned offset)
>+{
>+	Elf32_Dyn *dyn = (void *)ehdr + offset;
>+
>+	for(; dyn->d_tag != DT_NULL; dyn++)
>+		switch(dyn->d_tag) {
>+		case DT_PLTGOT:
>+		case DT_HASH:
>+		case DT_STRTAB:
>+		case DT_SYMTAB:
>+		case DT_RELA:
>+		case DT_INIT:
>+		case DT_FINI:
>+		case DT_REL:
>+		case DT_JMPREL:
>+		case DT_VERSYM:
>+		case DT_VERDEF:
>+		case DT_VERNEED:
>+			dyn->d_un.d_val += VDSO_HIGH_BASE;
>+		}
>+}

While there's a certain level of control on what DT_* may appear in the
vDSO, not even considering other than the above types seems fragile to
me. Since future additions to the set are supposedly following a fixed
scheme (distinguishing pointers and values via the low bit when below
OLD_DT_LOOS, and using sub-ranges when between DT_HIOS and
OLD_DT_HIOS), at least also handling those would seem like a good
idea, as would warning about unrecognized types.

Also, even though it shouldn't matter for the final result, if doing things
spec-conforming here you should use d_un.d_ptr.

In addition to Roland's remarks about missing symbol table relocation, I
would also assume section headers, if present, should be relocated.

Jan
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