Date:   Fri, 7 Jun 2019 05:50:22 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Edward Cree <ecree@...arflare.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 13/15] x86/static_call: Add inline static call
 implementation for x86-64

> On Jun 5, 2019, at 6:08 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> From: Josh Poimboeuf <jpoimboe@...hat.com>
> 
> Add the inline static call implementation for x86-64.  For each key, a
> temporary trampoline is created, named __static_call_tramp_<key>.  The
> trampoline has an indirect jump to the destination function.
> 
> Objtool uses the trampoline naming convention to detect all the call
> sites.  It then annotates those call sites in the .static_call_sites
> section.
> 
> During boot (and module init), the call sites are patched to call
> directly into the destination function.  The temporary trampoline is
> then no longer used.
> 
> Cc: x86@...nel.org
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Julia Cartwright <julia@...com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Jason Baron <jbaron@...mai.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: David Laight <David.Laight@...LAB.COM>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F62188c62f6dda49ca2e20629ee8e5a62a6c0b500.1543200841.git.jpoimboe%40redhat.com&amp;data=02%7C01%7Cnamit%40vmware.com%7C3a349bb2a7e042ef9d9d08d6e9b8fc2d%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636953378066316039&amp;sdata=J%2BsCYwRi8GpP5GrJaLo8nM5jN2KNZlfwq7RDuKok%2FmE%3D&amp;reserved=0
> ---
> arch/x86/Kconfig                                |    3 
> arch/x86/include/asm/static_call.h              |   28 ++++-
> arch/x86/kernel/asm-offsets.c                   |    6 +
> arch/x86/kernel/static_call.c                   |   12 +-
> include/linux/static_call.h                     |    2 
> tools/objtool/Makefile                          |    3 
> tools/objtool/check.c                           |  125 +++++++++++++++++++++++-
> tools/objtool/check.h                           |    2 
> tools/objtool/elf.h                             |    1 
> tools/objtool/include/linux/static_call_types.h |   19 +++
> tools/objtool/sync-check.sh                     |    1 
> 11 files changed, 193 insertions(+), 9 deletions(-)
> create mode 100644 tools/objtool/include/linux/static_call_types.h
> 
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -199,6 +199,7 @@ config X86
> 	select HAVE_STACKPROTECTOR		if CC_HAS_SANE_STACKPROTECTOR
> 	select HAVE_STACK_VALIDATION		if X86_64
> 	select HAVE_STATIC_CALL
> +	select HAVE_STATIC_CALL_INLINE		if HAVE_STACK_VALIDATION
> 	select HAVE_RSEQ
> 	select HAVE_SYSCALL_TRACEPOINTS
> 	select HAVE_UNSTABLE_SCHED_CLOCK
> @@ -213,6 +214,7 @@ config X86
> 	select RTC_MC146818_LIB
> 	select SPARSE_IRQ
> 	select SRCU
> +	select STACK_VALIDATION			if HAVE_STACK_VALIDATION && (HAVE_STATIC_CALL_INLINE || RETPOLINE)
> 	select SYSCTL_EXCEPTION_TRACE
> 	select THREAD_INFO_IN_TASK
> 	select USER_STACKTRACE_SUPPORT
> @@ -439,7 +441,6 @@ config GOLDFISH
> config RETPOLINE
> 	bool "Avoid speculative indirect branches in kernel"
> 	default y
> -	select STACK_VALIDATION if HAVE_STACK_VALIDATION
> 	help
> 	  Compile kernel with the retpoline compiler options to guard against
> 	  kernel-to-user data leaks by avoiding speculative indirect
> --- a/arch/x86/include/asm/static_call.h
> +++ b/arch/x86/include/asm/static_call.h
> @@ -2,6 +2,20 @@
> #ifndef _ASM_STATIC_CALL_H
> #define _ASM_STATIC_CALL_H
> 
> +#include <asm/asm-offsets.h>
> +
> +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> +
> +/*
> + * This trampoline is only used during boot / module init, so it's safe to use
> + * the indirect branch without a retpoline.
> + */
> +#define __ARCH_STATIC_CALL_TRAMP_JMP(key, func)				\
> +	ANNOTATE_RETPOLINE_SAFE						\
> +	"jmpq *" __stringify(key) "+" __stringify(SC_KEY_func) "(%rip) \n"
> +
> +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */
> +
> /*
>  * Manually construct a 5-byte direct JMP to prevent the assembler from
>  * optimizing it into a 2-byte JMP.
> @@ -12,9 +26,19 @@
> 	".long " #func " - " __ARCH_STATIC_CALL_JMP_LABEL(key) "\n"	\
> 	__ARCH_STATIC_CALL_JMP_LABEL(key) ":"
> 
> +#endif /* !CONFIG_HAVE_STATIC_CALL_INLINE */
> +
> /*
> - * This is a permanent trampoline which does a direct jump to the function.
> - * The direct jump get patched by static_call_update().
> + * For CONFIG_HAVE_STATIC_CALL_INLINE, this is a temporary trampoline which
> + * uses the current value of the key->func pointer to do an indirect jump to
> + * the function.  This trampoline is only used during boot, before the call
> + * sites get patched by static_call_update().  The name of this trampoline has
> + * a magical aspect: objtool uses it to find static call sites so it can create
> + * the .static_call_sites section.
> + *
> + * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
> + * does a direct jump to the function.  The direct jump gets patched by
> + * static_call_update().
>  */
> #define ARCH_DEFINE_STATIC_CALL_TRAMP(key, func)			\
> 	asm(".pushsection .text, \"ax\"				\n"	\
> --- a/arch/x86/kernel/asm-offsets.c
> +++ b/arch/x86/kernel/asm-offsets.c
> @@ -12,6 +12,7 @@
> #include <linux/hardirq.h>
> #include <linux/suspend.h>
> #include <linux/kbuild.h>
> +#include <linux/static_call.h>
> #include <asm/processor.h>
> #include <asm/thread_info.h>
> #include <asm/sigframe.h>
> @@ -104,4 +105,9 @@ static void __used common(void)
> 	OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
> 	OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);
> 	OFFSET(TSS_sp2, tss_struct, x86_tss.sp2);
> +
> +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> +	BLANK();
> +	OFFSET(SC_KEY_func, static_call_key, func);
> +#endif
> }
> --- a/arch/x86/kernel/static_call.c
> +++ b/arch/x86/kernel/static_call.c
> @@ -10,16 +10,22 @@
> void arch_static_call_transform(void *site, void *tramp, void *func)
> {
> 	unsigned char opcodes[CALL_INSN_SIZE];
> -	unsigned char insn_opcode;
> +	unsigned char insn_opcode, expected;
> 	unsigned long insn;
> 	s32 dest_relative;
> 
> 	mutex_lock(&text_mutex);
> 
> -	insn = (unsigned long)tramp;
> +	if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) {
> +		insn = (unsigned long)site;
> +		expected = 0xE8; /* CALL */

RELATIVECALL_OPCODE ?

> +	} else {
> +		insn = (unsigned long)tramp;
> +		expected = 0xE9; /* JMP */

RELATIVEJUMP_OPCODE ?

( I did not review the objtool parts )

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