From dc438db5828fd6a379648ab8735ee73a8e40865a Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Sun, 23 Jan 2022 20:28:39 +0100 Subject: [PATCH] ARM: ftrace: use trampolines to keep .init.text in branching range Kernel images that are large in comparison to the range of a direct branch may fail to work as expected with ftrace, as patching a direct branch to one of the core ftrace routines may not be possible from the .init.text section, if it is emitted too far away from the normal .text section. This is more likely to affect Thumb2 builds, given that its range is only -/+ 16 MiB (as opposed to ARM which has -/+ 32 MiB), but may occur in either ISA. To work around this, add a couple of trampolines to .init.text and swap these in when the ftrace patching code is operating on callers in .init.text. Signed-off-by: Ard Biesheuvel Reviewed-by: Nick Desaulniers Reviewed-by: Linus Walleij Reviewed-by: Steven Rostedt (Google) --- arch/arm/kernel/entry-ftrace.S | 16 ++++++++++++++++ arch/arm/kernel/ftrace.c | 23 ++++++++++++++++++++--- 2 files changed, 36 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index dca12a09322a..237d435e29aa 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -270,3 +270,19 @@ ENTRY(ftrace_stub) .Lftrace_stub: ret lr ENDPROC(ftrace_stub) + +#ifdef CONFIG_DYNAMIC_FTRACE + + __INIT + + .macro init_tramp, dst:req +ENTRY(\dst\()_from_init) + ldr pc, =\dst +ENDPROC(\dst\()_from_init) + .endm + + init_tramp ftrace_caller +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS + init_tramp ftrace_regs_caller +#endif +#endif diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c index 811cadf7eefc..74d3913f5590 100644 --- a/arch/arm/kernel/ftrace.c +++ b/arch/arm/kernel/ftrace.c @@ -62,9 +62,20 @@ static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec) return NOP; } -static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr) +void ftrace_caller_from_init(void); +void ftrace_regs_caller_from_init(void); + +static unsigned long __ref adjust_address(struct dyn_ftrace *rec, + unsigned long addr) { - return addr; + if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE) || + system_state >= SYSTEM_FREEING_INITMEM || + likely(!is_kernel_inittext(rec->ip))) + return addr; + if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) || + addr == (unsigned long)&ftrace_caller) + return (unsigned long)&ftrace_caller_from_init; + return (unsigned long)&ftrace_regs_caller_from_init; } int ftrace_arch_code_modify_prepare(void) @@ -200,7 +211,13 @@ int ftrace_make_nop(struct module *mod, #endif new = ftrace_nop_replace(rec); - ret = ftrace_modify_code(ip, old, new, true); + /* + * Locations in .init.text may call __gnu_mcount_mc via a linker + * emitted veneer if they are too far away from its implementation, and + * so validation may fail spuriously in such cases. Let's work around + * this by omitting those from validation. + */ + ret = ftrace_modify_code(ip, old, new, !is_kernel_inittext(ip)); return ret; } -- 2.25.1