linux-kernel - [PATCH v1 18/22] powerpc/ftrace: Don't use copy_from_kernel_nofault() in module_trampoline

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Message-Id: <a69258e6e1f5d966b80e51c8ac9aec5696b4c344.1648131740.git.christophe.leroy@csgroup.eu>
Date:   Thu, 24 Mar 2022 15:30:08 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 18/22] powerpc/ftrace: Don't use copy_from_kernel_nofault() in module_trampoline_target()

module_trampoline_target() is quite a hot path used when
activating/deactivating function tracer.

Avoid the heavy copy_from_kernel_nofault() by doing four calls
to copy_inst_from_kernel_nofault().

Use __copy_inst_from_kernel_nofault() for the 3 last calls. First call
is done to copy_from_kernel_nofault() to check address is within
kernel space. No risk to wrap out the top of kernel space because the
last page is never mapped so if address is in last page the first copy
will fails and the other ones will never be performed.

And also make it notrace just like all functions that call it.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/module_32.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
index 2aa368ce21c9..1282cfd672f2 100644
--- a/arch/powerpc/kernel/module_32.c
+++ b/arch/powerpc/kernel/module_32.c
@@ -289,13 +289,19 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
 }
 
 #ifdef CONFIG_FUNCTION_TRACER
-int module_trampoline_target(struct module *mod, unsigned long addr,
-			     unsigned long *target)
+notrace 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)))
+	if (copy_inst_from_kernel_nofault(jmp, (void *)addr))
+		return -EFAULT;
+	if (__copy_inst_from_kernel_nofault(jmp + 1, (void *)addr + 4))
+		return -EFAULT;
+	if (__copy_inst_from_kernel_nofault(jmp + 2, (void *)addr + 8))
+		return -EFAULT;
+	if (__copy_inst_from_kernel_nofault(jmp + 3, (void *)addr + 12))
 		return -EFAULT;
 
 	/* verify that this is what we expect it to be */
-- 
2.35.1