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Message-ID: <20170729010632.GE84665@google.com>
Date: Fri, 28 Jul 2017 18:06:32 -0700
From: Matthias Kaehlcke <mka@...omium.org>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>,
Chris J Arges <chris.j.arges@...onical.com>,
Borislav Petkov <bp@...e.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
"x86@...nel.org" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Douglas Anderson <dianders@...omium.org>,
Michael Davidson <md@...gle.com>,
Greg Hackmann <ghackmann@...gle.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Stephen Hines <srhines@...gle.com>,
Kees Cook <keescook@...omium.org>,
Arnd Bergmann <arnd@...db.de>,
Bernhard Rosenkränzer
<Bernhard.Rosenkranzer@...aro.org>
Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in
get_user() inline asm"
El Fri, Jul 28, 2017 at 07:55:21PM -0500 Josh Poimboeuf ha dit:
> On Fri, Jul 28, 2017 at 05:38:52PM -0700, Matthias Kaehlcke wrote:
> > El Thu, Jul 20, 2017 at 03:56:52PM -0500 Josh Poimboeuf ha dit:
> >
> > > On Thu, Jul 20, 2017 at 06:30:24PM +0300, Andrey Ryabinin wrote:
> > > > FWIW bellow is my understanding of what's going on.
> > > >
> > > > It seems clang treats local named register almost the same as ordinary
> > > > local variables.
> > > > The only difference is that before reading the register variable clang
> > > > puts variable's value into the specified register.
> > > >
> > > > So clang just assigns stack slot for the variable __sp where it's
> > > > going to keep variable's value.
> > > > But since __sp is unitialized (we haven't assign anything to it), the
> > > > value of the __sp is some garbage from stack.
> > > > inline asm specifies __sp as input, so clang assumes that it have to
> > > > load __sp into 'rsp' because inline asm is going to use
> > > > it. And it just loads garbage from stack into 'rsp'
> > > >
> > > > In fact, such behavior (I mean storing the value on stack and loading
> > > > into reg before the use) is very useful.
> > > > Clang's behavior allows to keep the value assigned to the
> > > > call-clobbered register across the function calls.
> > > >
> > > > Unlike clang, gcc assigns value to the register right away and doesn't
> > > > store the value anywhere else. So if the reg is
> > > > call clobbered register you have to be absolutely sure that there is
> > > > no subsequent function call that might clobber the register.
> > > >
> > > > E.g. see some real examples
> > > > https://patchwork.kernel.org/patch/4111971/ or 98d4ded60bda("msm: scm:
> > > > Fix improper register assignment").
> > > > These bugs shouldn't happen with clang.
> > > >
> > > > But the global named register works slightly differently in clang. For
> > > > the global, the value is just the value of the register itself,
> > > > whatever it is. Read/write from global named register is just like
> > > > direct read/write to the register
> > >
> > > Thanks, that clears up a lot of the confusion for me.
> > >
> > > Still, unfortunately, I don't think that's going to work for GCC.
> > > Changing the '__sp' register variable to global in the header file
> > > causes it to make a *bunch* of changes across the kernel, even in
> > > functions which don't do inline asm. It seems to be disabling some
> > > optimizations across the board.
> > >
> > > I do have another idea, which is to replace all uses of
> > >
> > > asm(" ... call foo ... " : outputs : inputs : clobbers);
> > >
> > > with a new ASM_CALL macro:
> > >
> > > ASM_CALL(" ... call foo ... ", outputs, inputs, clobbers);
> > >
> > > Then the compiler differences can be abstracted out, with GCC adding
> > > "sp" as an output constraint and clang doing nothing (for now).
> >
> > The idea sounds interesting, however I see two issues with ASM_CALL():
> >
> > Inline assembly expects the individual elements of outputs, inputs and
> > clobbers to be comma separated, and so does the macro for it's
> > parameters.
>
> I think this isn't a problem, see the (untested and unfinished) patch
> below for an idea of how the arguments can be handled.
Good point!
> > The assembler template can refer to the position of output and input
> > operands, adding "sp" as output changes the positions of the inputs
> > wrt to the clang version.
>
> True, though I think we could convert all ASM_CALL users to use named
> operands instead of the (bug-prone) numbered ones. It would be an
> improvement regardless.
Agreed, that sounds like a good solution and a desirable improvement.
> > Not sure how to move forward from here. Not even using an ugly #ifdef
> > seems to be a halfway reasonable solution, since get_user() isn't the
> > only place using this construct and #ifdefs would result in highly
> > redundant macros in multiple places.
>
> I still think ASM_CALL might work. The below patch is what I came up
> with last week before I got pulled into some other work. I'll be out on
> vacation next week but I hope to finish the patch after that.
Thanks for working on this.
Enjoy your vacation!
Matthias
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 1b020381ab38..5da4bcbeebab 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -216,14 +216,14 @@ static inline int alternatives_text_reserved(void *start, void *end)
> * Otherwise, old function is used.
> */
> #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
> - output, input...) \
> + output, input, clobbers...) \
> { \
> - register void *__sp asm(_ASM_SP); \
> - asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
> - "call %P[new2]", feature2) \
> - : output, "+r" (__sp) \
> - : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
> - [new2] "i" (newfunc2), ## input); \
> + ASM_CALL(ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1, \
> + "call %P[new2]", feature2), \
> + ARGS(output), \
> + ARGS([old] "i" (oldfunc), [new1] "i" (newfunc1), \
> + [new2] "i" (newfunc2), ARGS(input)), \
> + ## clobbers); \
> }
>
> /*
> diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> index b4a0d43248cf..21adcc8e739f 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -45,8 +45,8 @@ static inline void clear_page(void *page)
> clear_page_rep, X86_FEATURE_REP_GOOD,
> clear_page_erms, X86_FEATURE_ERMS,
> "=D" (page),
> - "0" (page)
> - : "memory", "rax", "rcx");
> + "0" (page),
> + ARGS("memory", "rax", "rcx"));
> }
>
> void copy_page(void *to, void *from);
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index cb976bab6299..2a585b799a3e 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -471,8 +471,7 @@ int paravirt_disable_iospace(void);
> */
> #ifdef CONFIG_X86_32
> #define PVOP_VCALL_ARGS \
> - unsigned long __eax = __eax, __edx = __edx, __ecx = __ecx; \
> - register void *__sp asm("esp")
> + unsigned long __eax = __eax, __edx = __edx, __ecx = __ecx;
> #define PVOP_CALL_ARGS PVOP_VCALL_ARGS
>
> #define PVOP_CALL_ARG1(x) "a" ((unsigned long)(x))
> @@ -492,8 +491,7 @@ int paravirt_disable_iospace(void);
> /* [re]ax isn't an arg, but the return val */
> #define PVOP_VCALL_ARGS \
> unsigned long __edi = __edi, __esi = __esi, \
> - __edx = __edx, __ecx = __ecx, __eax = __eax; \
> - register void *__sp asm("rsp")
> + __edx = __edx, __ecx = __ecx, __eax = __eax;
> #define PVOP_CALL_ARGS PVOP_VCALL_ARGS
>
> #define PVOP_CALL_ARG1(x) "D" ((unsigned long)(x))
> @@ -541,24 +539,24 @@ int paravirt_disable_iospace(void);
> /* This is 32-bit specific, but is okay in 64-bit */ \
> /* since this condition will never hold */ \
> if (sizeof(rettype) > sizeof(unsigned long)) { \
> - asm volatile(pre \
> - paravirt_alt(PARAVIRT_CALL) \
> - post \
> - : call_clbr, "+r" (__sp) \
> - : paravirt_type(op), \
> - paravirt_clobber(clbr), \
> - ##__VA_ARGS__ \
> - : "memory", "cc" extra_clbr); \
> + ASM_CALL(pre \
> + paravirt_alt(PARAVIRT_CALL) \
> + post, \
> + ARGS(call_clbr), \
> + ARGS(paravirt_type(op), \
> + paravirt_clobber(clbr), \
> + ##__VA_ARGS__), \
> + ARGS("memory", "cc" extra_clbr)); \
> __ret = (rettype)((((u64)__edx) << 32) | __eax); \
> } else { \
> - asm volatile(pre \
> - paravirt_alt(PARAVIRT_CALL) \
> - post \
> - : call_clbr, "+r" (__sp) \
> - : paravirt_type(op), \
> - paravirt_clobber(clbr), \
> - ##__VA_ARGS__ \
> - : "memory", "cc" extra_clbr); \
> + ASM_CALL(pre \
> + paravirt_alt(PARAVIRT_CALL) \
> + post, \
> + ARGS(call_clbr), \
> + ARGS(paravirt_type(op), \
> + paravirt_clobber(clbr), \
> + ##__VA_ARGS__), \
> + ARGS("memory", "cc" extra_clbr)); \
> __ret = (rettype)(__eax & PVOP_RETMASK(rettype)); \
> } \
> __ret; \
> @@ -578,14 +576,14 @@ int paravirt_disable_iospace(void);
> ({ \
> PVOP_VCALL_ARGS; \
> PVOP_TEST_NULL(op); \
> - asm volatile(pre \
> - paravirt_alt(PARAVIRT_CALL) \
> - post \
> - : call_clbr, "+r" (__sp) \
> - : paravirt_type(op), \
> - paravirt_clobber(clbr), \
> - ##__VA_ARGS__ \
> - : "memory", "cc" extra_clbr); \
> + ASM_CALL(pre \
> + paravirt_alt(PARAVIRT_CALL) \
> + post, \
> + ARGS(call_clbr), \
> + ARGS(paravirt_type(op), \
> + paravirt_clobber(clbr), \
> + ##__VA_ARGS__), \
> + ARGS("memory", "cc" extra_clbr)); \
> })
>
> #define __PVOP_VCALL(op, pre, post, ...) \
> diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
> index ec1f3c651150..19a034cbde37 100644
> --- a/arch/x86/include/asm/preempt.h
> +++ b/arch/x86/include/asm/preempt.h
> @@ -102,16 +102,14 @@ static __always_inline bool should_resched(int preempt_offset)
> extern asmlinkage void ___preempt_schedule(void);
> # define __preempt_schedule() \
> ({ \
> - register void *__sp asm(_ASM_SP); \
> - asm volatile ("call ___preempt_schedule" : "+r"(__sp)); \
> + ASM_CALL("call ___preempt_schedule",,); \
> })
>
> extern asmlinkage void preempt_schedule(void);
> extern asmlinkage void ___preempt_schedule_notrace(void);
> # define __preempt_schedule_notrace() \
> ({ \
> - register void *__sp asm(_ASM_SP); \
> - asm volatile ("call ___preempt_schedule_notrace" : "+r"(__sp)); \
> + ASM_CALL("call ___preempt_schedule_notrace",,); \
> })
> extern asmlinkage void preempt_schedule_notrace(void);
> #endif
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 550bc4ab0df4..2bbfb777c8bb 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -677,20 +677,19 @@ static inline void sync_core(void)
> * Like all of Linux's memory ordering operations, this is a
> * compiler barrier as well.
> */
> - register void *__sp asm(_ASM_SP);
>
> #ifdef CONFIG_X86_32
> - asm volatile (
> + ASM_CALL(
> "pushfl\n\t"
> "pushl %%cs\n\t"
> "pushl $1f\n\t"
> "iret\n\t"
> - "1:"
> - : "+r" (__sp) : : "memory");
> + "1:",
> + , , "memory");
> #else
> unsigned int tmp;
>
> - asm volatile (
> + ASM_CALL(
> UNWIND_HINT_SAVE
> "mov %%ss, %0\n\t"
> "pushq %q0\n\t"
> @@ -702,8 +701,8 @@ static inline void sync_core(void)
> "pushq $1f\n\t"
> "iretq\n\t"
> UNWIND_HINT_RESTORE
> - "1:"
> - : "=&r" (tmp), "+r" (__sp) : : "cc", "memory");
> + "1:",
> + "=&r" (tmp), , ARGS("cc", "memory"));
> #endif
> }
>
> diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
> index a34e0d4b957d..9d20f4fb5d7c 100644
> --- a/arch/x86/include/asm/rwsem.h
> +++ b/arch/x86/include/asm/rwsem.h
> @@ -99,25 +99,24 @@ static inline bool __down_read_trylock(struct rw_semaphore *sem)
> /*
> * lock for writing
> */
> -#define ____down_write(sem, slow_path) \
> -({ \
> - long tmp; \
> - struct rw_semaphore* ret; \
> - register void *__sp asm(_ASM_SP); \
> - \
> - asm volatile("# beginning down_write\n\t" \
> - LOCK_PREFIX " xadd %1,(%4)\n\t" \
> - /* adds 0xffff0001, returns the old value */ \
> - " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
> - /* was the active mask 0 before? */\
> - " jz 1f\n" \
> - " call " slow_path "\n" \
> - "1:\n" \
> - "# ending down_write" \
> - : "+m" (sem->count), "=d" (tmp), "=a" (ret), "+r" (__sp) \
> - : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \
> - : "memory", "cc"); \
> - ret; \
> +#define ____down_write(sem, slow_path) \
> +({ \
> + long tmp; \
> + struct rw_semaphore* ret; \
> + \
> + ASM_CALL("# beginning down_write\n\t" \
> + LOCK_PREFIX " xadd %1,(%3)\n\t" \
> + /* adds 0xffff0001, returns the old value */ \
> + " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
> + /* was the active mask 0 before? */ \
> + " jz 1f\n" \
> + " call " slow_path "\n" \
> + "1:\n" \
> + "# ending down_write", \
> + ARGS("+m" (sem->count), "=d" (tmp), "=a" (ret)), \
> + ARGS("a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS)), \
> + ARGS("memory", "cc")); \
> + ret; \
> })
>
> static inline void __down_write(struct rw_semaphore *sem)
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 184eb9894dae..c7be076ee703 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -166,12 +166,11 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
> ({ \
> int __ret_gu; \
> register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
> - register void *__sp asm(_ASM_SP); \
> __chk_user_ptr(ptr); \
> might_fault(); \
> - asm volatile("call __get_user_%P4" \
> - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \
> - : "0" (ptr), "i" (sizeof(*(ptr)))); \
> + ASM_CALL("call __get_user_%P3", \
> + ARGS("=a" (__ret_gu), "=r" (__val_gu)), \
> + ARGS("0" (ptr), "i" (sizeof(*(ptr))))); \
> (x) = (__force __typeof__(*(ptr))) __val_gu; \
> __builtin_expect(__ret_gu, 0); \
> })
> diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
> index b16f6a1d8b26..8b63e2cb1eaf 100644
> --- a/arch/x86/include/asm/uaccess_64.h
> +++ b/arch/x86/include/asm/uaccess_64.h
> @@ -38,10 +38,9 @@ copy_user_generic(void *to, const void *from, unsigned len)
> X86_FEATURE_REP_GOOD,
> copy_user_enhanced_fast_string,
> X86_FEATURE_ERMS,
> - ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
> - "=d" (len)),
> - "1" (to), "2" (from), "3" (len)
> - : "memory", "rcx", "r8", "r9", "r10", "r11");
> + ARGS("=a" (ret), "=D" (to), "=S" (from), "=d" (len)),
> + ARGS("1" (to), "2" (from), "3" (len)),
> + ARGS("memory", "rcx", "r8", "r9", "r10", "r11"));
> return ret;
> }
>
> diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
> index 11071fcd630e..2feddeeec1d1 100644
> --- a/arch/x86/include/asm/xen/hypercall.h
> +++ b/arch/x86/include/asm/xen/hypercall.h
> @@ -114,9 +114,8 @@ extern struct { char _entry[32]; } hypercall_page[];
> register unsigned long __arg3 asm(__HYPERCALL_ARG3REG) = __arg3; \
> register unsigned long __arg4 asm(__HYPERCALL_ARG4REG) = __arg4; \
> register unsigned long __arg5 asm(__HYPERCALL_ARG5REG) = __arg5; \
> - register void *__sp asm(_ASM_SP);
>
> -#define __HYPERCALL_0PARAM "=r" (__res), "+r" (__sp)
> +#define __HYPERCALL_0PARAM "=r" (__res)
> #define __HYPERCALL_1PARAM __HYPERCALL_0PARAM, "+r" (__arg1)
> #define __HYPERCALL_2PARAM __HYPERCALL_1PARAM, "+r" (__arg2)
> #define __HYPERCALL_3PARAM __HYPERCALL_2PARAM, "+r" (__arg3)
> @@ -146,10 +145,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_0ARG(); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_0PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER0); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_0PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER0); \
> (type)__res; \
> })
>
> @@ -157,10 +156,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_1ARG(a1); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_1PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER1); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_1PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER1); \
> (type)__res; \
> })
>
> @@ -168,10 +167,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_2ARG(a1, a2); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_2PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER2); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_2PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER2); \
> (type)__res; \
> })
>
> @@ -179,10 +178,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_3ARG(a1, a2, a3); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_3PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER3); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_3PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER3); \
> (type)__res; \
> })
>
> @@ -190,10 +189,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_4ARG(a1, a2, a3, a4); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_4PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER4); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_4PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER4); \
> (type)__res; \
> })
>
> @@ -201,10 +200,10 @@ extern struct { char _entry[32]; } hypercall_page[];
> ({ \
> __HYPERCALL_DECLS; \
> __HYPERCALL_5ARG(a1, a2, a3, a4, a5); \
> - asm volatile (__HYPERCALL \
> - : __HYPERCALL_5PARAM \
> - : __HYPERCALL_ENTRY(name) \
> - : __HYPERCALL_CLOBBER5); \
> + ASM_CALL(__HYPERCALL, \
> + __HYPERCALL_5PARAM, \
> + __HYPERCALL_ENTRY(name), \
> + __HYPERCALL_CLOBBER5); \
> (type)__res; \
> })
>
> @@ -218,10 +217,10 @@ privcmd_call(unsigned call,
> __HYPERCALL_5ARG(a1, a2, a3, a4, a5);
>
> stac();
> - asm volatile("call *%[call]"
> - : __HYPERCALL_5PARAM
> - : [call] "a" (&hypercall_page[call])
> - : __HYPERCALL_CLOBBER5);
> + ASM_CALL("call *%[call]",
> + __HYPERCALL_5PARAM,
> + [call] "a" (&hypercall_page[call]),
> + __HYPERCALL_CLOBBER5);
> clac();
>
> return (long)__res;
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index fb0055953fbc..4d0d326029a7 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5284,16 +5284,15 @@ static void fetch_possible_mmx_operand(struct x86_emulate_ctxt *ctxt,
>
> static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
> {
> - register void *__sp asm(_ASM_SP);
> ulong flags = (ctxt->eflags & EFLAGS_MASK) | X86_EFLAGS_IF;
>
> if (!(ctxt->d & ByteOp))
> fop += __ffs(ctxt->dst.bytes) * FASTOP_SIZE;
>
> - asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
> - : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
> - [fastop]"+S"(fop), "+r"(__sp)
> - : "c"(ctxt->src2.val));
> + ASM_CALL("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n",
> + ARGS("+a"(ctxt->dst.val), "+d"(ctxt->src.val),
> + [flags]"+D"(flags), [fastop]"+S"(fop)),
> + ARGS("c"(ctxt->src2.val)));
>
> ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) | (flags & EFLAGS_MASK);
> if (!fop) /* exception is returned in fop variable */
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ffd469ecad57..d42806ad3c9c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8671,7 +8671,6 @@ static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
> static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
> {
> u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
> - register void *__sp asm(_ASM_SP);
>
> if ((exit_intr_info & (INTR_INFO_VALID_MASK | INTR_INFO_INTR_TYPE_MASK))
> == (INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR)) {
> @@ -8686,7 +8685,7 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
> vector = exit_intr_info & INTR_INFO_VECTOR_MASK;
> desc = (gate_desc *)vmx->host_idt_base + vector;
> entry = gate_offset(*desc);
> - asm volatile(
> + ASM_CALL(
> #ifdef CONFIG_X86_64
> "mov %%" _ASM_SP ", %[sp]\n\t"
> "and $0xfffffffffffffff0, %%" _ASM_SP "\n\t"
> @@ -8695,16 +8694,14 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
> #endif
> "pushf\n\t"
> __ASM_SIZE(push) " $%c[cs]\n\t"
> - "call *%[entry]\n\t"
> - :
> + "call *%[entry]\n\t",
> #ifdef CONFIG_X86_64
> - [sp]"=&r"(tmp),
> + [sp]"=&r"(tmp)
> #endif
> - "+r"(__sp)
> - :
> - [entry]"r"(entry),
> - [ss]"i"(__KERNEL_DS),
> - [cs]"i"(__KERNEL_CS)
> + ,
> + ARGS([entry]"r"(entry),
> + [ss]"i"(__KERNEL_DS),
> + [cs]"i"(__KERNEL_CS))
> );
> }
> }
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 2a1fa10c6a98..ca642ac3a390 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -802,7 +802,6 @@ no_context(struct pt_regs *regs, unsigned long error_code,
> if (is_vmalloc_addr((void *)address) &&
> (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
> address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
> - register void *__sp asm("rsp");
> unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *);
> /*
> * We're likely to be running with very little stack space
> @@ -814,13 +813,12 @@ no_context(struct pt_regs *regs, unsigned long error_code,
> * and then double-fault, though, because we're likely to
> * break the console driver and lose most of the stack dump.
> */
> - asm volatile ("movq %[stack], %%rsp\n\t"
> - "call handle_stack_overflow\n\t"
> - "1: jmp 1b"
> - : "+r" (__sp)
> - : "D" ("kernel stack overflow (page fault)"),
> - "S" (regs), "d" (address),
> - [stack] "rm" (stack));
> + ASM_CALL("movq %[stack], %%rsp\n\t"
> + "call handle_stack_overflow\n\t"
> + "1: jmp 1b",
> + ,
> + ARGS("D" ("kernel stack overflow (page fault)"),
> + "S" (regs), "d" (address), [stack] "rm" (stack)));
> unreachable();
> }
> #endif
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 3f8c88e29a46..3a57f32a0bfd 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -589,4 +589,18 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
> (_________p1); \
> })
>
> +#define ARGS(args...) args
> +
> +#ifdef CONFIG_FRAME_POINTER
> +
> +#define ASM_CALL(str, outputs, inputs, clobbers...) \
> + asm volatile(str : outputs : inputs : "sp", ## clobbers)
> +
> +#else
> +
> +#define ASM_CALL(str, outputs, inputs, clobbers...) \
> + asm volatile(str : outputs : inputs : clobbers);
> +
> +#endif
> +
> #endif /* __LINUX_COMPILER_H */
> diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
> index 6a1af43862df..766a00ebf80c 100644
> --- a/tools/objtool/Documentation/stack-validation.txt
> +++ b/tools/objtool/Documentation/stack-validation.txt
> @@ -193,13 +193,8 @@ they mean, and suggestions for how to fix them.
>
> If it's a GCC-compiled .c file, the error may be because the function
> uses an inline asm() statement which has a "call" instruction. An
> - asm() statement with a call instruction must declare the use of the
> - stack pointer in its output operand. For example, on x86_64:
> -
> - register void *__sp asm("rsp");
> - asm volatile("call func" : "+r" (__sp));
> -
> - Otherwise the stack frame may not get created before the call.
> + asm() statement with a call instruction must use the ASM_CALL macro,
> + which forces the frame pointer to be saved before the call.
>
>
> 2. file.o: warning: objtool: .text+0x53: unreachable instruction
> @@ -221,7 +216,7 @@ they mean, and suggestions for how to fix them.
> change ENDPROC to END.
>
>
> -4. file.o: warning: objtool: func(): can't find starting instruction
> +3. file.o: warning: objtool: func(): can't find starting instruction
> or
> file.o: warning: objtool: func()+0x11dd: can't decode instruction
>
> @@ -230,7 +225,7 @@ they mean, and suggestions for how to fix them.
> section like .data or .rodata.
>
>
> -5. file.o: warning: objtool: func()+0x6: unsupported instruction in callable function
> +4. file.o: warning: objtool: func()+0x6: unsupported instruction in callable function
>
> This is a kernel entry/exit instruction like sysenter or iret. Such
> instructions aren't allowed in a callable function, and are most
> @@ -239,7 +234,7 @@ they mean, and suggestions for how to fix them.
> annotated with the unwind hint macros in asm/unwind_hints.h.
>
>
> -6. file.o: warning: objtool: func()+0x26: sibling call from callable instruction with modified stack frame
> +5. file.o: warning: objtool: func()+0x26: sibling call from callable instruction with modified stack frame
>
> This is a dynamic jump or a jump to an undefined symbol. Objtool
> assumed it's a sibling call and detected that the frame pointer
> @@ -253,7 +248,7 @@ they mean, and suggestions for how to fix them.
> the unwind hint macros in asm/unwind_hints.h.
>
>
> -7. file: warning: objtool: func()+0x5c: stack state mismatch
> +6. file: warning: objtool: func()+0x5c: stack state mismatch
>
> The instruction's frame pointer state is inconsistent, depending on
> which execution path was taken to reach the instruction.
> @@ -270,7 +265,7 @@ they mean, and suggestions for how to fix them.
> asm/unwind_hints.h.
>
>
> -8. file.o: warning: objtool: funcA() falls through to next function funcB()
> +7. file.o: warning: objtool: funcA() falls through to next function funcB()
>
> This means that funcA() doesn't end with a return instruction or an
> unconditional jump, and that objtool has determined that the function
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