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x86, relocs: Ignore relocations in .notes section

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[ Upstream commit aaa8736370 ]

When building with CONFIG_XEN_PV=y, .text symbols are emitted into
the .notes section so that Xen can find the "startup_xen" entry point.
This information is used prior to booting the kernel, so relocations
are not useful. In fact, performing relocations against the .notes
section means that the KASLR base is exposed since /sys/kernel/notes
is world-readable.

To avoid leaking the KASLR base without breaking unprivileged tools that
are expecting to read /sys/kernel/notes, skip performing relocations in
the .notes section. The values readable in .notes are then identical to
those found in System.map.

Reported-by: Guixiong Wei <guixiongwei@gmail.com>
Closes: https://lore.kernel.org/all/20240218073501.54555-1-guixiongwei@gmail.com/
Fixes: 5ead97c84f ("xen: Core Xen implementation")
Fixes: da1a679cde ("Add /sys/kernel/notes")
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Kees Cook 2024-02-27 09:51:12 -08:00 committed by Sasha Levin
parent 39ee8d8c26
commit 5cb59db49c
1 changed files with 8 additions and 0 deletions
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8
arch/x86/tools/relocs.c
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@ -653,6 +653,14 @@ static void print_absolute_relocs(void)
if (!(sec_applies->shdr.sh_flags & SHF_ALLOC)) {
continue;
}
/*
* Do not perform relocations in .notes section; any
* values there are meant for pre-boot consumption (e.g.
* startup_xen).
*/
if (sec_applies->shdr.sh_type == SHT_NOTE) {
continue;
}
sh_symtab = sec_symtab->symtab;
sym_strtab = sec_symtab->link->strtab;
for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Rel); j++) {