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Message-ID: <c3dcdb3c-3883-7913-510b-8c39d0e0390b@oracle.com>
Date: Fri, 3 Apr 2020 10:08:44 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, Paul McKenney <paulmck@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
"Steven Rostedt (VMware)" <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Frederic Weisbecker <frederic@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Brian Gerst <brgerst@...il.com>,
Juergen Gross <jgross@...e.com>,
Peter Zijlstra <peterz@...radead.org>,
Tom Lendacky <thomas.lendacky@....com>,
Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [RESEND][patch V3 03/23] vmlinux.lds.h: Create section for
protection against instrumentation
On 3/20/20 6:59 PM, Thomas Gleixner wrote:
> Some code pathes, especially the low level entry code, must be protected
> against instrumentation for various reasons:
>
> - Low level entry code can be a fragile beast, especially on x86.
>
> - With NO_HZ_FULL RCU state needs to be established before using it.
>
> Having a dedicated section for such code allows to validate with tooling
> that no unsafe functions are invoked.
>
> Add the .noinstr.text section and the noinstr attribute to mark
> functions. noinstr implies notrace. Kprobes will gain a section check
> later.
>
> Provide also two sets of markers:
>
> - instr_begin()/end()
>
> This is used to mark code inside in a noinstr function which calls
> into regular instrumentable text section as safe.
>
> - noinstr_call_begin()/end()
>
> Same as above but used to mark indirect calls which cannot be tracked by
> tooling and need to be audited manually.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> include/asm-generic/sections.h | 3 +++
> include/asm-generic/vmlinux.lds.h | 4 ++++
> include/linux/compiler.h | 24 ++++++++++++++++++++++++
> include/linux/compiler_types.h | 4 ++++
> scripts/mod/modpost.c | 2 +-
> 5 files changed, 36 insertions(+), 1 deletion(-)
>
> --- a/include/asm-generic/sections.h
> +++ b/include/asm-generic/sections.h
> @@ -53,6 +53,9 @@ extern char __ctors_start[], __ctors_end
> /* Start and end of .opd section - used for function descriptors. */
> extern char __start_opd[], __end_opd[];
>
> +/* Start and end of instrumentation protected text section */
> +extern char __noinstr_text_start[], __noinstr_text_end[];
> +
> extern __visible const void __nosave_begin, __nosave_end;
>
> /* Function descriptor handling (if any). Override in asm/sections.h */
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -550,6 +550,10 @@
> #define TEXT_TEXT \
> ALIGN_FUNCTION(); \
> *(.text.hot TEXT_MAIN .text.fixup .text.unlikely) \
> + ALIGN_FUNCTION(); \
> + __noinstr_text_start = .; \
> + *(.noinstr.text) \
> + __noinstr_text_end = .; \
> *(.text..refcount) \
> *(.ref.text) \
> MEM_KEEP(init.text*) \
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -120,12 +120,36 @@ void ftrace_likely_update(struct ftrace_
> /* Annotate a C jump table to allow objtool to follow the code flow */
> #define __annotate_jump_table __section(.rodata..c_jump_table)
>
> +/* Begin/end of an instrumentation safe region */
> +#define instr_begin() ({ \
> + asm volatile("%c0:\n\t" \
> + ".pushsection .discard.instr_begin\n\t" \
> + ".long %c0b - .\n\t" \
> + ".popsection\n\t" : : "i" (__COUNTER__)); \
> +})
> +
> +#define instr_end() ({ \
> + asm volatile("%c0:\n\t" \
> + ".pushsection .discard.instr_end\n\t" \
> + ".long %c0b - .\n\t" \
> + ".popsection\n\t" : : "i" (__COUNTER__)); \
> +})
> +
> #else
> #define annotate_reachable()
> #define annotate_unreachable()
> #define __annotate_jump_table
> +#define instr_begin() do { } while(0)
> +#define instr_end() do { } while(0)
> #endif
>
> +/*
> + * Annotation for audited indirect calls. Distinct from instr_begin() on
> + * purpose because the called function has to be noinstr as well.
> + */
> +#define noinstr_call_begin() instr_begin()
> +#define noinstr_call_end() instr_end()
> +
Do you have an example of noinstr_call_begin()/end() usage? I have some
hard time figuring out why we need to call them out.
Thanks,
alex.
> #ifndef ASM_UNREACHABLE
> # define ASM_UNREACHABLE
> #endif
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -118,6 +118,10 @@ struct ftrace_likely_data {
> #define notrace __attribute__((__no_instrument_function__))
> #endif
>
> +/* Section for code which can't be instrumented at all */
> +#define noinstr \
> + noinline notrace __attribute((__section__(".noinstr.text")))
> +
> /*
> * it doesn't make sense on ARM (currently the only user of __naked)
> * to trace naked functions because then mcount is called without
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -953,7 +953,7 @@ static void check_section(const char *mo
>
> #define DATA_SECTIONS ".data", ".data.rel"
> #define TEXT_SECTIONS ".text", ".text.unlikely", ".sched.text", \
> - ".kprobes.text", ".cpuidle.text"
> + ".kprobes.text", ".cpuidle.text", ".noinstr.text"
> #define OTHER_TEXT_SECTIONS ".ref.text", ".head.text", ".spinlock.text", \
> ".fixup", ".entry.text", ".exception.text", ".text.*", \
> ".coldtext"
>
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