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 <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 5ead97c84fa7 ("xen: Core Xen implementation")
Fixes: da1a679cde9b ("Add /sys/kernel/notes")
Reviewed-by: Juergen Gross <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
---
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: [email protected]
Cc: "H. Peter Anvin" <[email protected]>
Cc: "Peter Zijlstra (Intel)" <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Kristen Carlson Accardi <[email protected]>
v2: switch to a SHT_NOTE check (jgross)
v1: https://lore.kernel.org/all/[email protected]/
---
arch/x86/tools/relocs.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index a3bae2b24626..b029fb81ebee 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -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++) {
--
2.34.1