linux-kernel - [PATCH v1 3/5] powerpc/ftrace: Add module_trampoline

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Message-Id: <42345f464fb465f0fc76f3090e250be8fc1729f0.1635423081.git.christophe.leroy@csgroup.eu>
Date:   Thu, 28 Oct 2021 14:24:03 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        live-patching@...r.kernel.org
Subject: [PATCH v1 3/5] powerpc/ftrace: Add module_trampoline_target() for PPC32

module_trampoline_target() is used by __ftrace_modify_call().

Implement it for PPC32 so that CONFIG_DYNAMIC_FTRACE_WITH_REGS
can be activated on PPC32 as well.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/module_32.c    | 25 ++++++++++++++++++++
 arch/powerpc/kernel/trace/ftrace.c | 37 ++++--------------------------
 2 files changed, 29 insertions(+), 33 deletions(-)

diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
index f417afc08d33..5dedd76346b2 100644
--- a/arch/powerpc/kernel/module_32.c
+++ b/arch/powerpc/kernel/module_32.c
@@ -273,6 +273,31 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
 }
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+int module_trampoline_target(struct module *mod, unsigned long addr,
+			     unsigned long *target)
+{
+	unsigned int jmp[4];
+
+	/* Find where the trampoline jumps to */
+	if (copy_from_kernel_nofault(jmp, (void *)addr, sizeof(jmp)))
+		return -EFAULT;
+
+	/* verify that this is what we expect it to be */
+	if ((jmp[0] & 0xffff0000) != PPC_RAW_LIS(_R12, 0) ||
+	    (jmp[1] & 0xffff0000) != PPC_RAW_ADDI(_R12, _R12, 0) ||
+	    jmp[2] != PPC_RAW_MTCTR(_R12) ||
+	    jmp[3] != PPC_RAW_BCTR())
+		return -EINVAL;
+
+	addr = (jmp[1] & 0xffff) | ((jmp[0] & 0xffff) << 16);
+	if (addr & 0x8000)
+		addr -= 0x10000;
+
+	*target = addr;
+
+	return 0;
+}
+
 int module_finalize_ftrace(struct module *module, const Elf_Shdr *sechdrs)
 {
 	module->arch.tramp = do_plt_call(module->core_layout.base,
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index d89c5df4f206..c1d54c18e912 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -222,9 +222,8 @@ __ftrace_make_nop(struct module *mod,
 		  struct dyn_ftrace *rec, unsigned long addr)
 {
 	struct ppc_inst op;
-	unsigned int jmp[4];
 	unsigned long ip = rec->ip;
-	unsigned long tramp;
+	unsigned long tramp, ptr;
 
 	if (copy_from_kernel_nofault(&op, (void *)ip, MCOUNT_INSN_SIZE))
 		return -EFAULT;
@@ -238,41 +237,13 @@ __ftrace_make_nop(struct module *mod,
 	/* lets find where the pointer goes */
 	tramp = find_bl_target(ip, op);
 
-	/*
-	 * On PPC32 the trampoline looks like:
-	 *  0x3d, 0x80, 0x00, 0x00  lis r12,sym@ha
-	 *  0x39, 0x8c, 0x00, 0x00  addi r12,r12,sym@l
-	 *  0x7d, 0x89, 0x03, 0xa6  mtctr r12
-	 *  0x4e, 0x80, 0x04, 0x20  bctr
-	 */
-
-	pr_devel("ip:%lx jumps to %lx", ip, tramp);
-
 	/* Find where the trampoline jumps to */
-	if (copy_from_kernel_nofault(jmp, (void *)tramp, sizeof(jmp))) {
-		pr_err("Failed to read %lx\n", tramp);
+	if (module_trampoline_target(mod, tramp, &ptr)) {
+		pr_err("Failed to get trampoline target\n");
 		return -EFAULT;
 	}
 
-	pr_devel(" %08x %08x ", jmp[0], jmp[1]);
-
-	/* verify that this is what we expect it to be */
-	if (((jmp[0] & 0xffff0000) != 0x3d800000) ||
-	    ((jmp[1] & 0xffff0000) != 0x398c0000) ||
-	    (jmp[2] != 0x7d8903a6) ||
-	    (jmp[3] != 0x4e800420)) {
-		pr_err("Not a trampoline\n");
-		return -EINVAL;
-	}
-
-	tramp = (jmp[1] & 0xffff) |
-		((jmp[0] & 0xffff) << 16);
-	if (tramp & 0x8000)
-		tramp -= 0x10000;
-
-	pr_devel(" %lx ", tramp);
-
-	if (tramp != addr) {
+	if (ptr != addr) {
 		pr_err("Trampoline location %08lx does not match addr\n",
 		       tramp);
 		return -EINVAL;
-- 
2.31.1