From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 3eefdf9d1e406f3da47470b2854347009ffcb6fa ]
The branch range checks in ftrace_make_call() and ftrace_make_nop() are incorrect, erroneously permitting a forwards branch of 128M and erroneously rejecting a backwards branch of 128M.
This is because both functions calculate the offset backwards, calculating the offset *from* the target *to* the branch, rather than the other way around as the later comparisons expect.
If an out-of-range branch were erroeously permitted, this would later be rejected by aarch64_insn_gen_branch_imm() as branch_imm_common() checks the bounds correctly, resulting in warnings and the placement of a BRK instruction. Note that this can only happen for a forwards branch of exactly 128M, and so the caller would need to be exactly 128M bytes below the relevant ftrace trampoline.
If an in-range branch were erroeously rejected, then:
* For modules when CONFIG_ARM64_MODULE_PLTS=y, this would result in the use of a PLT entry, which is benign.
Note that this is the common case, as this is selected by CONFIG_RANDOMIZE_BASE (and therefore RANDOMIZE_MODULE_REGION_FULL), which distributions typically seelct. This is also selected by CONFIG_ARM64_ERRATUM_843419.
* For modules when CONFIG_ARM64_MODULE_PLTS=n, this would result in internal ftrace failures.
* For core kernel text, this would result in internal ftrace failues.
Note that for this to happen, the kernel text would need to be at least 128M bytes in size, and typical configurations are smaller tha this.
Fix this by calculating the offset *from* the branch *to* the target in both functions.
Fixes: f8af0b364e24 ("arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()") Fixes: e71a4e1bebaf ("arm64: ftrace: add support for far branches to dynamic ftrace") Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Ard Biesheuvel ardb@kernel.org Cc: Will Deacon will@kernel.org Tested-by: "Ivan T. Ivanov" iivanov@suse.de Reviewed-by: Chengming Zhou zhouchengming@bytedance.com Reviewed-by: Ard Biesheuvel ardb@kernel.org Link: https://lore.kernel.org/r/20220614080944.1349146-2-mark.rutland@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/ftrace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 86a5cf9bc19a..e21a01b99999 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -83,7 +83,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) { unsigned long pc = rec->ip; u32 old, new; - long offset = (long)pc - (long)addr; + long offset = (long)addr - (long)pc;
if (offset < -SZ_128M || offset >= SZ_128M) { struct module *mod; @@ -182,7 +182,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long pc = rec->ip; bool validate = true; u32 old = 0, new; - long offset = (long)pc - (long)addr; + long offset = (long)addr - (long)pc;
if (offset < -SZ_128M || offset >= SZ_128M) { u32 replaced;