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Message-Id: <20180313205945.245105-22-thgarnie@google.com>
Date: Tue, 13 Mar 2018 13:59:39 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kate Stewart <kstewart@...uxfoundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Philippe Ombredanne <pombredanne@...b.com>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Matthias Kaehlcke <mka@...omium.org>,
Kees Cook <keescook@...omium.org>,
Tom Lendacky <thomas.lendacky@....com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Borislav Petkov <bp@...en8.de>,
Borislav Petkov <bp@...e.de>,
"Rafael J . Wysocki" <rjw@...ysocki.net>,
Len Brown <len.brown@...el.com>,
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Cc: x86@...nel.org,
linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
xen-devel@...ts.xenproject.org,
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kernel-hardening@...ts.openwall.com
Subject: [PATCH v2 21/27] x86/ftrace: Adapt function tracing for PIE support
When using -fPIE/PIC with function tracing, the compiler generates a
call through the GOT (call *__fentry__@...PCREL). This instruction
takes 6 bytes instead of 5 on the usual relative call.
If PIE is enabled, replace the 6th byte of the GOT call by a 1-byte nop
so ftrace can handle the previous 5-bytes as before.
Position Independent Executable (PIE) support will allow to extended the
KASLR randomization range below the -2G memory limit.
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
arch/x86/include/asm/ftrace.h | 6 +++--
arch/x86/include/asm/sections.h | 4 ++++
arch/x86/kernel/ftrace.c | 42 +++++++++++++++++++++++++++++++--
3 files changed, 48 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 09ad88572746..61fa02d81b95 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -25,9 +25,11 @@ extern void __fentry__(void);
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
/*
- * addr is the address of the mcount call instruction.
- * recordmcount does the necessary offset calculation.
+ * addr is the address of the mcount call instruction. PIE has always a
+ * byte added to the start of the function.
*/
+ if (IS_ENABLED(CONFIG_X86_PIE))
+ addr -= 1;
return addr;
}
diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index d6baf23782bc..cad292f62eed 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -12,4 +12,8 @@ extern struct exception_table_entry __stop___ex_table[];
extern char __end_rodata_hpage_align[];
#endif
+#if defined(CONFIG_X86_PIE)
+extern char __start_got[], __end_got[];
+#endif
+
#endif /* _ASM_X86_SECTIONS_H */
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 01ebcb6f263e..21bde498f1a9 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -102,7 +102,7 @@ static const unsigned char *ftrace_nop_replace(void)
static int
ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
- unsigned const char *new_code)
+ unsigned const char *new_code)
{
unsigned char replaced[MCOUNT_INSN_SIZE];
@@ -135,6 +135,44 @@ ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
return 0;
}
+/* Bytes before call GOT offset */
+const unsigned char got_call_preinsn[] = { 0xff, 0x15 };
+
+static int
+ftrace_modify_initial_code(unsigned long ip, unsigned const char *old_code,
+ unsigned const char *new_code)
+{
+ unsigned char replaced[MCOUNT_INSN_SIZE + 1];
+
+ ftrace_expected = old_code;
+
+ /*
+ * If PIE is not enabled or no GOT call was found, default to the
+ * original approach to code modification.
+ */
+ if (!IS_ENABLED(CONFIG_X86_PIE)
+ || probe_kernel_read(replaced, (void *)ip, sizeof(replaced))
+ || memcmp(replaced, got_call_preinsn, sizeof(got_call_preinsn)))
+ return ftrace_modify_code_direct(ip, old_code, new_code);
+
+ /*
+ * Build a nop slide with a 5-byte nop and 1-byte nop to keep the ftrace
+ * hooking algorithm working with the expected 5 bytes instruction.
+ */
+ memcpy(replaced, new_code, MCOUNT_INSN_SIZE);
+ replaced[MCOUNT_INSN_SIZE] = ideal_nops[1][0];
+
+ ip = text_ip_addr(ip);
+
+ if (probe_kernel_write((void *)ip, replaced, sizeof(replaced)))
+ return -EPERM;
+
+ sync_core();
+
+ return 0;
+
+}
+
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
@@ -153,7 +191,7 @@ int ftrace_make_nop(struct module *mod,
* just modify the code directly.
*/
if (addr == MCOUNT_ADDR)
- return ftrace_modify_code_direct(rec->ip, old, new);
+ return ftrace_modify_initial_code(rec->ip, old, new);
ftrace_expected = NULL;
--
2.16.2.660.g709887971b-goog
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