[PATCH stable 4.9 3/3] ARM: 9079/1: ftrace: Add MODULE_PLTS support

22 Sep 2021

From: Alexander Sverdlin alexander.sverdlin@nokia.com
commit 79f32b221b18c15a98507b101ef4beb52444cc6f upstream
Teach ftrace_make_call() and ftrace_make_nop() about PLTs.
Teach PLT code about FTRACE and all its callbacks.
Otherwise the following might happen:
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../arch/arm/kernel/insn.c:14 __arm_gen_branch+0x83/0x8c()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c03143cf>] (__arm_gen_branch+0x83/0x8c)
[<c03143cf>] (__arm_gen_branch) from [<c0314337>] (ftrace_make_nop+0xf/0x24)
[<c0314337>] (ftrace_make_nop) from [<c038ebcb>] (ftrace_process_locs+0x27b/0x3e8)
[<c038ebcb>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcc ]---
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1b1/0x234()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c038e87d>] (ftrace_bug+0x1b1/0x234)
[<c038e87d>] (ftrace_bug) from [<c038ebd5>] (ftrace_process_locs+0x285/0x3e8)
[<c038ebd5>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcd ]---
ftrace failed to modify [<e9ef7006>] 0xe9ef7006
actual: 02:f0:3b:fa
ftrace record flags: 0
(0) expected tramp: c0314265
Signed-off-by: Alexander Sverdlin alexander.sverdlin@nokia.com
Signed-off-by: Russell King rmk+kernel@armlinux.org.uk
Signed-off-by: Florian Fainelli f.fainelli@gmail.com
---
 arch/arm/include/asm/ftrace.h |  3 +++
 arch/arm/include/asm/module.h |  1 +
 arch/arm/kernel/ftrace.c      | 45 +++++++++++++++++++++++++++++------
 arch/arm/kernel/module-plts.c | 44 ++++++++++++++++++++++++++++++----
 4 files changed, 82 insertions(+), 11 deletions(-)

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 22b73112b75f..1c30be0f5dd0 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -14,6 +14,9 @@ struct dyn_arch_ftrace {
 #ifdef CONFIG_OLD_MCOUNT
    bool	old_mcount;
 #endif
+#ifdef CONFIG_ARM_MODULE_PLTS
+	struct module *mod;
+#endif
 };
static inline unsigned long ftrace_call_adjust(unsigned long addr)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 2e9872a22359..3cfbe8181224 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -29,6 +29,7 @@ struct plt_entries {
struct mod_plt_sec {
    struct elf32_shdr	*plt;
+	struct plt_entries	*plt_ent;
    int			plt_count;
 };
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index a95bc0a02fd8..b1cf37fec354 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -95,9 +95,10 @@ int ftrace_arch_code_modify_post_process(void)
    return 0;
 }
-static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
+static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr,
+					 bool warn)
 {
-	return arm_gen_branch_link(pc, addr, true);
+	return arm_gen_branch_link(pc, addr, warn);
 }
static int ftrace_modify_code(unsigned long pc, unsigned long old,
@@ -136,14 +137,14 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
    int ret;
pc = (unsigned long)&ftrace_call;
-	new = ftrace_call_replace(pc, (unsigned long)func);
+	new = ftrace_call_replace(pc, (unsigned long)func, true);
ret = ftrace_modify_code(pc, 0, new, false);
#ifdef CONFIG_OLD_MCOUNT
    if (!ret) {
    	pc = (unsigned long)&ftrace_call_old;
-		new = ftrace_call_replace(pc, (unsigned long)func);
+		new = ftrace_call_replace(pc, (unsigned long)func, true);
ret = ftrace_modify_code(pc, 0, new, false);
    }
@@ -156,9 +157,21 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
    unsigned long new, old;
    unsigned long ip = rec->ip;
+	unsigned long aaddr = adjust_address(rec, addr);
+	struct module *mod = NULL;
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+	mod = rec->arch.mod;
+#endif
old = ftrace_nop_replace(rec);
-	new = ftrace_call_replace(ip, adjust_address(rec, addr));
+	new = ftrace_call_replace(ip, aaddr, !mod);
+#ifdef CONFIG_ARM_MODULE_PLTS
+	if (!new && mod) {
+		aaddr = get_module_plt(mod, ip, aaddr);
+		new = ftrace_call_replace(ip, aaddr, true);
+	}
+#endif
return ftrace_modify_code(rec->ip, old, new, true);
 }
@@ -166,12 +179,29 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 int ftrace_make_nop(struct module *mod,
    	    struct dyn_ftrace *rec, unsigned long addr)
 {
+	unsigned long aaddr = adjust_address(rec, addr);
    unsigned long ip = rec->ip;
    unsigned long old;
    unsigned long new;
    int ret;
-	old = ftrace_call_replace(ip, adjust_address(rec, addr));
+#ifdef CONFIG_ARM_MODULE_PLTS
+	/* mod is only supplied during module loading */
+	if (!mod)
+		mod = rec->arch.mod;
+	else
+		rec->arch.mod = mod;
+#endif
+
+	old = ftrace_call_replace(ip, aaddr,
+				  !IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || !mod);
+#ifdef CONFIG_ARM_MODULE_PLTS
+	if (!old && mod) {
+		aaddr = get_module_plt(mod, ip, aaddr);
+		old = ftrace_call_replace(ip, aaddr, true);
+	}
+#endif
+
    new = ftrace_nop_replace(rec);
    ret = ftrace_modify_code(ip, old, new, true);
@@ -179,7 +209,8 @@ int ftrace_make_nop(struct module *mod,
    if (ret == -EINVAL && addr == MCOUNT_ADDR) {
    	rec->arch.old_mcount = true;
-		old = ftrace_call_replace(ip, adjust_address(rec, addr));
+		old = ftrace_call_replace(ip, adjust_address(rec, addr),
+					  !IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || !mod);
    	new = ftrace_nop_replace(rec);
    	ret = ftrace_modify_code(ip, old, new, true);
    }
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index f272711c411f..6804a145be11 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -7,6 +7,7 @@
  */
#include <linux/elf.h>
+#include <linux/ftrace.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sort.h>
@@ -22,19 +23,52 @@
    					    (PLT_ENT_STRIDE - 8))
 #endif
+static const u32 fixed_plts[] = {
+#ifdef CONFIG_FUNCTION_TRACER
+	FTRACE_ADDR,
+	MCOUNT_ADDR,
+#endif
+};
+
 static bool in_init(const struct module *mod, unsigned long loc)
 {
    return loc - (u32)mod->init_layout.base < mod->init_layout.size;
 }
+static void prealloc_fixed(struct mod_plt_sec *pltsec, struct plt_entries *plt)
+{
+	int i;
+
+	if (!ARRAY_SIZE(fixed_plts) || pltsec->plt_count)
+		return;
+	pltsec->plt_count = ARRAY_SIZE(fixed_plts);
+
+	for (i = 0; i < ARRAY_SIZE(plt->ldr); ++i)
+		plt->ldr[i] = PLT_ENT_LDR;
+
+	BUILD_BUG_ON(sizeof(fixed_plts) > sizeof(plt->lit));
+	memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
+}
+
 u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
 {
    struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
    						  &mod->arch.init;
+	struct plt_entries *plt;
+	int idx;
+
+	/* cache the address, ELF header is available only during module load */
+	if (!pltsec->plt_ent)
+		pltsec->plt_ent = (struct plt_entries *)pltsec->plt->sh_addr;
+	plt = pltsec->plt_ent;
-	struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
-	int idx = 0;
+	prealloc_fixed(pltsec, plt);
+
+	for (idx = 0; idx < ARRAY_SIZE(fixed_plts); ++idx)
+		if (plt->lit[idx] == val)
+			return (u32)&plt->ldr[idx];
+	idx = 0;
    /*
     * Look for an existing entry pointing to 'val'. Given that the
     * relocations are sorted, this will be the last entry we allocated.
@@ -182,8 +216,8 @@ static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
    		      char *secstrings, struct module *mod)
 {
-	unsigned long core_plts = 0;
-	unsigned long init_plts = 0;
+	unsigned long core_plts = ARRAY_SIZE(fixed_plts);
+	unsigned long init_plts = ARRAY_SIZE(fixed_plts);
    Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
    Elf32_Sym *syms = NULL;
@@ -238,6 +272,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
    mod->arch.core.plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
    				       sizeof(struct plt_entries));
    mod->arch.core.plt_count = 0;
+	mod->arch.core.plt_ent = NULL;
mod->arch.init.plt->sh_type = SHT_NOBITS;
    mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
@@ -245,6 +280,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
    mod->arch.init.plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
    				       sizeof(struct plt_entries));
    mod->arch.init.plt_count = 0;
+	mod->arch.init.plt_ent = NULL;
pr_debug("%s: plt=%x, init.plt=%x\n", __func__,
    	 mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
-- 
2.25.1


    

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[PATCH stable 4.9 3/3] ARM: 9079/1: ftrace: Add MODULE_PLTS support