Linux-parisc archive on lore.kernel.org
 help / color / Atom feed
From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, amit.kachhap@arm.com,
	catalin.marinas@arm.com, deller@gmx.de, duwe@suse.de,
	James.Bottomley@HansenPartnership.com, james.morse@arm.com,
	jeyu@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com,
	linux-parisc@vger.kernel.org, mark.rutland@arm.com,
	mingo@redhat.com, peterz@infradead.org, rostedt@goodmis.org,
	svens@stackframe.org, takahiro.akashi@linaro.org,
	will@kernel.org
Subject: [PATCHv2 4/8] arm64: module/ftrace: intialize PLT at load time
Date: Tue, 29 Oct 2019 16:58:28 +0000
Message-ID: <20191029165832.33606-5-mark.rutland@arm.com> (raw)
In-Reply-To: <20191029165832.33606-1-mark.rutland@arm.com>

Currently we lazily-initialize a module's ftrace PLT at runtime when we
install the first ftrace call. To do so we have to apply a number of
sanity checks, transiently mark the module text as RW, and perform an
IPI as part of handling Neoverse-N1 erratum #1542419.

We only expect the ftrace trampoline to point at ftrace_caller() (AKA
FTRACE_ADDR), so let's simplify all of this by intializing the PLT at
module load time, before the module loader marks the module RO and
performs the intial I-cache maintenance for the module.

Thus we can rely on the module having been correctly intialized, and can
simplify the runtime work necessary to install an ftrace call in a
module. This will also allow for the removal of module_disable_ro().

Tested by forcing ftrace_make_call() to use the module PLT, and then
loading up a module after setting up ftrace with:

| echo ":mod:<module-name>" > set_ftrace_filter;
| echo function > current_tracer;
| modprobe <module-name>

Since FTRACE_ADDR is only defined when CONFIG_DYNAMIC_FTRACE is
selected, we wrap its use along with most of module_init_ftrace_plt()
with ifdeffery rather than using IS_ENABLED().

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/ftrace.c | 55 ++++++++++++----------------------------------
 arch/arm64/kernel/module.c | 32 +++++++++++++++++----------
 2 files changed, 35 insertions(+), 52 deletions(-)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 06e56b470315..822718eafdb4 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -73,10 +73,22 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 
 	if (offset < -SZ_128M || offset >= SZ_128M) {
 #ifdef CONFIG_ARM64_MODULE_PLTS
-		struct plt_entry trampoline, *dst;
 		struct module *mod;
 
 		/*
+		 * There is only one ftrace trampoline per module. For now,
+		 * this is not a problem since on arm64, all dynamic ftrace
+		 * invocations are routed via ftrace_caller(). This will need
+		 * to be revisited if support for multiple ftrace entry points
+		 * is added in the future, but for now, the pr_err() below
+		 * deals with a theoretical issue only.
+		 */
+		if (addr != FTRACE_ADDR) {
+			pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
+			return -EINVAL;
+		}
+
+		/*
 		 * On kernels that support module PLTs, the offset between the
 		 * branch instruction and its target may legally exceed the
 		 * range of an ordinary relative 'bl' opcode. In this case, we
@@ -93,46 +105,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 		if (WARN_ON(!mod))
 			return -EINVAL;
 
-		/*
-		 * There is only one ftrace trampoline per module. For now,
-		 * this is not a problem since on arm64, all dynamic ftrace
-		 * invocations are routed via ftrace_caller(). This will need
-		 * to be revisited if support for multiple ftrace entry points
-		 * is added in the future, but for now, the pr_err() below
-		 * deals with a theoretical issue only.
-		 *
-		 * Note that PLTs are place relative, and plt_entries_equal()
-		 * checks whether they point to the same target. Here, we need
-		 * to check if the actual opcodes are in fact identical,
-		 * regardless of the offset in memory so use memcmp() instead.
-		 */
-		dst = mod->arch.ftrace_trampoline;
-		trampoline = get_plt_entry(addr, dst);
-		if (memcmp(dst, &trampoline, sizeof(trampoline))) {
-			if (plt_entry_is_initialized(dst)) {
-				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
-				return -EINVAL;
-			}
-
-			/* point the trampoline to our ftrace entry point */
-			module_disable_ro(mod);
-			*dst = trampoline;
-			module_enable_ro(mod, true);
-
-			/*
-			 * Ensure updated trampoline is visible to instruction
-			 * fetch before we patch in the branch. Although the
-			 * architecture doesn't require an IPI in this case,
-			 * Neoverse-N1 erratum #1542419 does require one
-			 * if the TLB maintenance in module_enable_ro() is
-			 * skipped due to rodata_enabled. It doesn't seem worth
-			 * it to make it conditional given that this is
-			 * certainly not a fast-path.
-			 */
-			flush_icache_range((unsigned long)&dst[0],
-					   (unsigned long)&dst[1]);
-		}
-		addr = (unsigned long)dst;
+		addr = (unsigned long)mod->arch.ftrace_trampoline;
 #else /* CONFIG_ARM64_MODULE_PLTS */
 		return -EINVAL;
 #endif /* CONFIG_ARM64_MODULE_PLTS */
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 763a86d52fef..5f5bc3b94da7 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -9,6 +9,7 @@
 
 #include <linux/bitops.h>
 #include <linux/elf.h>
+#include <linux/ftrace.h>
 #include <linux/gfp.h>
 #include <linux/kasan.h>
 #include <linux/kernel.h>
@@ -485,24 +486,33 @@ static const Elf_Shdr *find_section(const Elf_Ehdr *hdr,
 	return NULL;
 }
 
+int module_init_ftrace_plt(const Elf_Ehdr *hdr,
+			   const Elf_Shdr *sechdrs,
+			   struct module *mod)
+{
+#if defined(CONFIG_ARM64_MODULE_PLTS) && defined(CONFIG_DYNAMIC_FTRACE)
+	const Elf_Shdr *s;
+	struct plt_entry *plt;
+
+	s = find_section(hdr, sechdrs, ".text.ftrace_trampoline");
+	if (!s)
+		return -ENOEXEC;
+
+	plt = (void *)s->sh_addr;
+	*plt = get_plt_entry(FTRACE_ADDR, plt);
+	mod->arch.ftrace_trampoline = plt;
+#endif
+	return 0;
+}
+
 int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)
 {
 	const Elf_Shdr *s;
-
 	s = find_section(hdr, sechdrs, ".altinstructions");
 	if (s)
 		apply_alternatives_module((void *)s->sh_addr, s->sh_size);
 
-#ifdef CONFIG_ARM64_MODULE_PLTS
-	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE)) {
-		s = find_section(hdr, sechdrs, ".text.ftrace_trampoline");
-		if (!s)
-			return -ENOEXEC;
-		me->arch.ftrace_trampoline = (void *)s->sh_addr;
-	}
-#endif
-
-	return 0;
+	return module_init_ftrace_plt(hdr, sechdrs, me);
 }
-- 
2.11.0


  parent reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29 16:58 [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS Mark Rutland
2019-10-29 16:58 ` [PATCHv2 1/8] ftrace: add ftrace_init_nop() Mark Rutland
2019-10-30 15:00   ` Miroslav Benes
2019-11-02 12:19   ` Amit Daniel Kachhap
2019-11-04 13:11     ` Steven Rostedt
2019-11-05  6:59       ` Amit Kachhap
2019-11-04 13:36     ` Mark Rutland
2019-11-05  6:47       ` Amit Kachhap
2019-11-06 14:15         ` Mark Rutland
2019-11-07  4:40           ` Amit Kachhap
2019-11-04 13:16   ` Steven Rostedt
2019-11-04 13:38     ` Mark Rutland
2019-11-04 13:53       ` Steven Rostedt
2019-10-29 16:58 ` [PATCHv2 2/8] module/ftrace: handle patchable-function-entry Mark Rutland
2019-10-30 15:03   ` Torsten Duwe
2019-10-31  9:02     ` Mark Rutland
2019-10-31 11:42       ` Torsten Duwe
2019-10-31 13:00         ` Mark Rutland
2019-11-04 13:28           ` Steven Rostedt
2019-11-04 14:00             ` Mark Rutland
2019-11-04 13:25   ` Steven Rostedt
2019-11-04 15:51   ` Mark Rutland
2019-11-04 20:58     ` Helge Deller
2019-11-05  8:59   ` Miroslav Benes
2019-10-29 16:58 ` [PATCHv2 3/8] arm64: module: rework special section handling Mark Rutland
2019-10-30 15:25   ` Miroslav Benes
2019-10-29 16:58 ` Mark Rutland [this message]
2019-11-02 12:20   ` [PATCHv2 4/8] arm64: module/ftrace: intialize PLT at load time Amit Daniel Kachhap
2019-11-04 13:55     ` Mark Rutland
2019-10-29 16:58 ` [PATCHv2 5/8] arm64: insn: add encoder for MOV (register) Mark Rutland
2019-10-29 16:58 ` [PATCHv2 6/8] arm64: asm-offsets: add S_FP Mark Rutland
2019-10-29 16:58 ` [PATCHv2 7/8] arm64: implement ftrace with regs Mark Rutland
2019-11-02 12:21   ` Amit Daniel Kachhap
2019-11-04 13:51     ` Mark Rutland
     [not found]   ` <CANW9uyug8WKN2fR-FmcW-C_OO_OQ_AvukM+BR7wqiJ9eFQMO9Q@mail.gmail.com>
2019-11-15  7:45     ` Torsten Duwe
2019-11-15 13:59     ` Mark Rutland
2019-10-29 16:58 ` [PATCHv2 8/8] arm64: ftrace: minimize ifdeffery Mark Rutland
2019-10-30 17:02 ` [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS Torsten Duwe
2019-10-31 17:16 ` Torsten Duwe
2019-11-01  9:08   ` Mark Rutland
2019-11-01 15:39 ` Sven Schnelle
2019-11-01 16:28   ` Mark Rutland
2019-11-02 12:12 ` Amit Daniel Kachhap
2019-11-04 12:56   ` Will Deacon
2019-11-04 13:03     ` Amit Kachhap
2019-11-04 14:04       ` Mark Rutland
2019-11-05  7:06         ` Amit Kachhap
2019-11-07 11:31 ` Catalin Marinas

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191029165832.33606-5-mark.rutland@arm.com \
    --to=mark.rutland@arm.com \
    --cc=James.Bottomley@HansenPartnership.com \
    --cc=amit.kachhap@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=deller@gmx.de \
    --cc=duwe@suse.de \
    --cc=james.morse@arm.com \
    --cc=jeyu@kernel.org \
    --cc=jpoimboe@redhat.com \
    --cc=jthierry@redhat.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-parisc@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=svens@stackframe.org \
    --cc=takahiro.akashi@linaro.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-parisc archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-parisc/0 linux-parisc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-parisc linux-parisc/ https://lore.kernel.org/linux-parisc \
		linux-parisc@vger.kernel.org
	public-inbox-index linux-parisc

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-parisc


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git