releases/5.0.8/arm64-ftrace-fix-inadvertent-bug-in-trampoline-check.patch

   1 From 5a3ae7b314a2259b1188b22b392f5eba01e443ee Mon Sep 17 00:00:00 2001
   2 From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
   3 Date: Sun, 7 Apr 2019 21:06:16 +0200
   4 Subject: arm64/ftrace: fix inadvertent BUG() in trampoline check
   5
   6 From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
   7
   8 commit 5a3ae7b314a2259b1188b22b392f5eba01e443ee upstream.
   9
  10 The ftrace trampoline code (which deals with modules loaded out of
  11 BL range of the core kernel) uses plt_entries_equal() to check whether
  12 the per-module trampoline equals a zero buffer, to decide whether the
  13 trampoline has already been initialized.
  14
  15 This triggers a BUG() in the opcode manipulation code, since we end
  16 up checking the ADRP offset of a 0x0 opcode, which is not an ADRP
  17 instruction.
  18
  19 So instead, add a helper to check whether a PLT is initialized, and
  20 call that from the frace code.
  21
  22 Cc: <stable@vger.kernel.org> # v5.0
  23 Fixes: bdb85cd1d206 ("arm64/module: switch to ADRP/ADD sequences for PLT entries")
  24 Acked-by: Mark Rutland <mark.rutland@arm.com>
  25 Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
  26 Signed-off-by: Will Deacon <will.deacon@arm.com>
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  28
  29 ---
  30  arch/arm64/include/asm/module.h |    5 +++++
  31  arch/arm64/kernel/ftrace.c      |    3 +--
  32  2 files changed, 6 insertions(+), 2 deletions(-)
  33
  34 --- a/arch/arm64/include/asm/module.h
  35 +++ b/arch/arm64/include/asm/module.h
  36 @@ -73,4 +73,9 @@ static inline bool is_forbidden_offset_f
  37  struct plt_entry get_plt_entry(u64 dst, void *pc);
  38  bool plt_entries_equal(const struct plt_entry *a, const struct plt_entry *b);
  39
  40 +static inline bool plt_entry_is_initialized(const struct plt_entry *e)
  41 +{
  42 +       return e->adrp || e->add || e->br;
  43 +}
  44 +
  45  #endif /* __ASM_MODULE_H */
  46 --- a/arch/arm64/kernel/ftrace.c
  47 +++ b/arch/arm64/kernel/ftrace.c
  48 @@ -107,8 +107,7 @@ int ftrace_make_call(struct dyn_ftrace *
  49                 trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
  50                 if (!plt_entries_equal(mod->arch.ftrace_trampoline,
  51                                        &trampoline)) {
  52 -                       if (!plt_entries_equal(mod->arch.ftrace_trampoline,
  53 -                                              &(struct plt_entry){})) {
  54 +                       if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {
  55                                 pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
  56                                 return -EINVAL;
  57                         }