From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit 5679b28142193a62f6af93249c0477be9f0c669b ]
Commit f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences") moved the alternatives replacement sequences into subsections, in order to keep the as close as possible to the code that they replace.
Unfortunately, this broke the logic in branch_insn_requires_update, which assumed that any branch into kernel executable code was a branch that required updating, which is no longer the case now that the code sequences that are patched in are in the same section as the patch site itself.
So the only way to discriminate branches that require updating and ones that don't is to check whether the branch targets the replacement sequence itself, and so we can drop the call to kernel_text_address() entirely.
Fixes: f7b93d42945c ("arm64/alternatives: use subsections for replacement sequences") Reported-by: Alexandru Elisei alexandru.elisei@arm.com Signed-off-by: Ard Biesheuvel ardb@kernel.org Tested-by: Alexandru Elisei alexandru.elisei@arm.com Link: https://lore.kernel.org/r/20200709125953.30918-1-ardb@kernel.org Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/alternative.c | 16 ++-------------- 1 file changed, 2 insertions(+), 14 deletions(-)
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index d1757ef1b1e74..73039949b5ce2 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -43,20 +43,8 @@ bool alternative_is_applied(u16 cpufeature) */ static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) { - unsigned long replptr; - - if (kernel_text_address(pc)) - return true; - - replptr = (unsigned long)ALT_REPL_PTR(alt); - if (pc >= replptr && pc <= (replptr + alt->alt_len)) - return false; - - /* - * Branching into *another* alternate sequence is doomed, and - * we're not even trying to fix it up. - */ - BUG(); + unsigned long replptr = (unsigned long)ALT_REPL_PTR(alt); + return !(pc >= replptr && pc <= (replptr + alt->alt_len)); }
#define align_down(x, a) ((unsigned long)(x) & ~(((unsigned long)(a)) - 1))