leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86/vdso: Hack to keep 64-bit Go programs working

Browse Source 
The Go runtime has a buggy vDSO parser that currently segfaults.
This writes an empty SHT_DYNSYM entry that causes Go's runtime to
malfunction by thinking that the vDSO is empty rather than
malfunctioning by running off the end and segfaulting.

This affects x86-64 only as far as we know, so we do not need this for
the i386 and x32 vdsos.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/d10618176c4bd39b457a5e85c497295c90cab1bc.1402620737.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Andy Lutomirski 2014-06-12 17:53:12 -07:00 committed by H. Peter Anvin
parent b4b31f6101
commit e0bf7b86da
3 changed files with 60 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
arch/x86/vdso/Makefile
View File

@ -15,12 +15,8 @@ vdso-install-$(VDSO32-y) += $(vdso32-images)
# files to link into the vdso
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
vobjs-$(VDSOX32-y) += $(vobjx32s-compat)
# Filter out x32 objects.
vobj64s := $(filter-out $(vobjx32s-compat),$(vobjs-y))
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vdso-fakesections.o
vobjs-nox32 := vdso-fakesections.o
# files to link into kernel
obj-y += vma.o
@ -34,7 +30,7 @@ vdso_img-$(VDSO32-y) += 32-sysenter
obj-$(VDSO32-y) += vdso32-setup.o
vobjs := $(foreach F,$(vobj64s),$(obj)/$F)
vobjs := $(foreach F,$(vobjs-y),$(obj)/$F)
$(obj)/vdso.o: $(obj)/vdso.so
@ -104,7 +100,13 @@ VDSO_LDFLAGS_vdsox32.lds = -Wl,-m,elf32_x86_64 \
-Wl,-z,max-page-size=4096 \
-Wl,-z,common-page-size=4096
vobjx32s-y := $(vobj64s:.o=-x32.o)
# 64-bit objects to re-brand as x32
vobjs64-for-x32 := $(filter-out $(vobjs-nox32),$(vobjs-y))
# x32-rebranded versions
vobjx32s-y := $(vobjs64-for-x32:.o=-x32.o)
# same thing, but in the output directory
vobjx32s := $(foreach F,$(vobjx32s-y),$(obj)/$F)
# Convert 64bit object file to x32 for x32 vDSO.

32
arch/x86/vdso/vdso-fakesections.c Normal file
View File

@ -0,0 +1,32 @@
/*
* Copyright 2014 Andy Lutomirski
* Subject to the GNU Public License, v.2
*
* Hack to keep broken Go programs working.
*
* The Go runtime had a couple of bugs: it would read the section table to try
* to figure out how many dynamic symbols there were (it shouldn't have looked
* at the section table at all) and, if there were no SHT_SYNDYM section table
* entry, it would use an uninitialized value for the number of symbols. As a
* workaround, we supply a minimal section table. vdso2c will adjust the
* in-memory image so that "vdso_fake_sections" becomes the section table.
*
* The bug was introduced by:
* https://code.google.com/p/go/source/detail?r=56ea40aac72b (2012-08-31)
* and is being addressed in the Go runtime in this issue:
* https://code.google.com/p/go/issues/detail?id=8197
*/
#ifndef __x86_64__
#error This hack is specific to the 64-bit vDSO
#endif
#include <linux/elf.h>
extern const __visible struct elf64_shdr vdso_fake_sections[];
const __visible struct elf64_shdr vdso_fake_sections[] = {
{
.sh_type = SHT_DYNSYM,
.sh_entsize = sizeof(Elf64_Sym),
}
};

23
arch/x86/vdso/vdso2c.h
View File

@ -18,6 +18,8 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
const char *secstrings;
uint64_t syms[NSYMS] = {};
uint64_t fake_sections_value = 0, fake_sections_size = 0;
Elf_Phdr *pt = (Elf_Phdr *)(addr + GET_LE(&hdr->e_phoff));
/* Walk the segment table. */
@ -84,6 +86,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
GET_LE(&symtab_hdr->sh_entsize) * i;
const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
GET_LE(&sym->st_name);
for (k = 0; k < NSYMS; k++) {
if (!strcmp(name, required_syms[k])) {
if (syms[k]) {
@ -93,6 +96,13 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
syms[k] = GET_LE(&sym->st_value);
}
}
if (!strcmp(name, "vdso_fake_sections")) {
if (fake_sections_value)
fail("duplicate vdso_fake_sections\n");
fake_sections_value = GET_LE(&sym->st_value);
fake_sections_size = GET_LE(&sym->st_size);
}
}
/* Validate mapping addresses. */
@ -112,11 +122,14 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
if (syms[sym_end_mapping] % 4096)
fail("end_mapping must be a multiple of 4096\n");
/* Remove sections. */
hdr->e_shoff = 0;
hdr->e_shentsize = 0;
hdr->e_shnum = 0;
hdr->e_shstrndx = SHN_UNDEF; /* SHN_UNDEF == 0 */
/* Remove sections or use fakes */
if (fake_sections_size % sizeof(Elf_Shdr))
fail("vdso_fake_sections size is not a multiple of %ld\n",
(long)sizeof(Elf_Shdr));
PUT_LE(&hdr->e_shoff, fake_sections_value);
PUT_LE(&hdr->e_shentsize, fake_sections_value ? sizeof(Elf_Shdr) : 0);
PUT_LE(&hdr->e_shnum, fake_sections_size / sizeof(Elf_Shdr));
PUT_LE(&hdr->e_shstrndx, SHN_UNDEF);
if (!name) {
fwrite(addr, load_size, 1, outfile);