x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG
authorPetr Pavlu <petr.pavlu@suse.com>
Tue, 11 Jul 2023 09:19:51 +0000 (11:19 +0200)
committerBorislav Petkov (AMD) <bp@alien8.de>
Mon, 14 Aug 2023 09:44:19 +0000 (11:44 +0200)
commit79cd2a11224eab86d6673fe8a11d2046ae9d2757
tree0ee936d47ffbfd103a1a109a87bcc794f7007f2d
parente9fbc47b818b964ddff5df5b2d5c0f5f32f4a147
x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

The linker script arch/x86/kernel/vmlinux.lds.S matches the thunk
sections ".text.__x86.*" from arch/x86/lib/retpoline.S as follows:

  .text {
    [...]
    TEXT_TEXT
    [...]
    __indirect_thunk_start = .;
    *(.text.__x86.*)
    __indirect_thunk_end = .;
    [...]
  }

Macro TEXT_TEXT references TEXT_MAIN which normally expands to only
".text". However, with CONFIG_LTO_CLANG, TEXT_MAIN becomes
".text .text.[0-9a-zA-Z_]*" which wrongly matches also the thunk
sections. The output layout is then different than expected. For
instance, the currently defined range [__indirect_thunk_start,
__indirect_thunk_end] becomes empty.

Prevent the problem by using ".." as the first separator, for example,
".text..__x86.indirect_thunk". This pattern is utilized by other
explicit section names which start with one of the standard prefixes,
such as ".text" or ".data", and that need to be individually selected in
the linker script.

  [ nathan: Fix conflicts with SRSO and fold in fix issue brought up by
    Andrew Cooper in post-review:
    https://lore.kernel.org/20230803230323.1478869-1-andrew.cooper3@citrix.com ]

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230711091952.27944-2-petr.pavlu@suse.com
arch/x86/kernel/vmlinux.lds.S
arch/x86/lib/retpoline.S
tools/objtool/check.c