Commit a7ed7b9d authored by panfan's avatar panfan Committed by Catalin Marinas
Browse files

arm64: ftrace: fix unreachable PLT for ftrace_caller in init_module with CONFIG_DYNAMIC_FTRACE 



On arm64, it has been possible for a module's sections to be placed more
than 128M away from each other since commit:

  commit 3e35d303 ("arm64: module: rework module VA range selection")

Due to this, an ftrace callsite in a module's .init.text section can be
out of branch range for the module's ftrace PLT entry (in the module's
.text section). Any attempt to enable tracing of that callsite will
result in a BRK being patched into the callsite, resulting in a fatal
exception when the callsite is later executed.

Fix this by adding an additional trampoline for .init.text, which will
be within range.

No additional trampolines are necessary due to the way a given
module's executable sections are packed together. Any executable
section beginning with ".init" will be placed in MOD_INIT_TEXT,
and any other executable section, including those beginning with ".exit",
 will be placed in MOD_TEXT.

Fixes: 3e35d303 ("arm64: module: rework module VA range selection")
Cc: <stable@vger.kernel.org> # 6.5.x
Signed-off-by: default avatarpanfan <panfan@qti.qualcomm.com>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20250905032236.3220885-1-panfan@qti.qualcomm.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent f3ef7110

arch/arm64/include/asm/module.h

+1 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ struct mod_arch_specific { 


	/* for CONFIG_DYNAMIC_FTRACE */

	struct plt_entry	*ftrace_trampolines;

	struct plt_entry	*init_ftrace_trampolines;

};



u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,

arch/arm64/include/asm/module.lds.h

+1 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ SECTIONS { 
	.plt 0 : { BYTE(0) }

	.init.plt 0 : { BYTE(0) }

	.text.ftrace_trampoline 0 : { BYTE(0) }

	.init.text.ftrace_trampoline 0 : { BYTE(0) }



#ifdef CONFIG_KASAN_SW_TAGS

	/*

arch/arm64/kernel/ftrace.c

+10 −3
Original line number Diff line number Diff line
@@ -258,10 +258,17 @@ int ftrace_update_ftrace_func(ftrace_func_t func) 
	return ftrace_modify_code(pc, 0, new, false);

}



static struct plt_entry *get_ftrace_plt(struct module *mod)

static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)

{

#ifdef CONFIG_MODULES

	struct plt_entry *plt = mod->arch.ftrace_trampolines;

	struct plt_entry *plt = NULL;



	if (within_module_mem_type(addr, mod, MOD_INIT_TEXT))

		plt = mod->arch.init_ftrace_trampolines;

	else if (within_module_mem_type(addr, mod, MOD_TEXT))

		plt = mod->arch.ftrace_trampolines;

	else

		return NULL;



	return &plt[FTRACE_PLT_IDX];

#else
@@ -332,7 +339,7 @@ static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, 
	if (WARN_ON(!mod))

		return false;



	plt = get_ftrace_plt(mod);

	plt = get_ftrace_plt(mod, pc);

	if (!plt) {

		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);

		return false;

arch/arm64/kernel/module-plts.c

+11 −1
Original line number Diff line number Diff line
@@ -283,7 +283,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
	unsigned long core_plts = 0;

	unsigned long init_plts = 0;

	Elf64_Sym *syms = NULL;

	Elf_Shdr *pltsec, *tramp = NULL;

	Elf_Shdr *pltsec, *tramp = NULL, *init_tramp = NULL;

	int i;



	/*
@@ -298,6 +298,9 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
		else if (!strcmp(secstrings + sechdrs[i].sh_name,

				 ".text.ftrace_trampoline"))

			tramp = sechdrs + i;

		else if (!strcmp(secstrings + sechdrs[i].sh_name,

				 ".init.text.ftrace_trampoline"))

			init_tramp = sechdrs + i;

		else if (sechdrs[i].sh_type == SHT_SYMTAB)

			syms = (Elf64_Sym *)sechdrs[i].sh_addr;

	}
@@ -363,5 +366,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 
		tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);

	}



	if (init_tramp) {

		init_tramp->sh_type = SHT_NOBITS;

		init_tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;

		init_tramp->sh_addralign = __alignof__(struct plt_entry);

		init_tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);

	}



	return 0;

}

arch/arm64/kernel/module.c

+11 −0
Original line number Diff line number Diff line
@@ -466,6 +466,17 @@ static int module_init_ftrace_plt(const Elf_Ehdr *hdr, 
	__init_plt(&plts[FTRACE_PLT_IDX], FTRACE_ADDR);



	mod->arch.ftrace_trampolines = plts;



	s = find_section(hdr, sechdrs, ".init.text.ftrace_trampoline");

	if (!s)

		return -ENOEXEC;



	plts = (void *)s->sh_addr;



	__init_plt(&plts[FTRACE_PLT_IDX], FTRACE_ADDR);



	mod->arch.init_ftrace_trampolines = plts;



#endif

	return 0;

}