Commit fa697140 authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Ingo Molnar

syscalls/x86: Use 'struct pt_regs' based syscall calling convention for 64-bit syscalls

Let's make use of ARCH_HAS_SYSCALL_WRAPPER=y on pure 64-bit x86-64 systems:

Each syscall defines a stub which takes struct pt_regs as its only
argument. It decodes just those parameters it needs, e.g:

	asmlinkage long sys_xyzzy(const struct pt_regs *regs)
	{
		return SyS_xyzzy(regs->di, regs->si, regs->dx);
	}

This approach avoids leaking random user-provided register content down
the call chain.

For example, for sys_recv() which is a 4-parameter syscall, the assembly
now is (in slightly reordered fashion):

	<sys_recv>:
		callq	<__fentry__>

		/* decode regs->di, ->si, ->dx and ->r10 */
		mov	0x70(%rdi),%rdi
		mov	0x68(%rdi),%rsi
		mov	0x60(%rdi),%rdx
		mov	0x38(%rdi),%rcx

		[ SyS_recv() is automatically inlined by the compiler,
		  as it is not [yet] used anywhere else ]
		/* clear %r9 and %r8, the 5th and 6th args */
		xor	%r9d,%r9d
		xor	%r8d,%r8d

		/* do the actual work */
		callq	__sys_recvfrom

		/* cleanup and return */
		cltq
		retq

The only valid place in an x86-64 kernel which rightfully calls
a syscall function on its own -- vsyscall -- needs to be modified
to pass struct pt_regs onwards as well.

To keep the syscall table generation working independent of
SYSCALL_PTREGS being enabled, the stubs are named the same as the
"original" syscall stubs, i.e. sys_*().

This patch is based on an original proof-of-concept

 | From: Linus Torvalds <torvalds@linux-foundation.org>
 | Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

and was split up and heavily modified by me, in particular to base it on
ARCH_HAS_SYSCALL_WRAPPER, to limit it to 64-bit-only for the time being,
and to update the vsyscall to the new calling convention.
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180405095307.3730-4-linux@dominikbrodowski.netSigned-off-by: Ingo Molnar's avatarIngo Molnar <mingo@kernel.org>
parent 1bd21c6c
......@@ -2954,3 +2954,8 @@ source "crypto/Kconfig"
source "arch/x86/kvm/Kconfig"
source "lib/Kconfig"
config SYSCALL_PTREGS
def_bool y
depends on X86_64 && !COMPAT
select ARCH_HAS_SYSCALL_WRAPPER
......@@ -284,9 +284,13 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
nr &= __SYSCALL_MASK;
if (likely(nr < NR_syscalls)) {
nr = array_index_nospec(nr, NR_syscalls);
#ifdef CONFIG_SYSCALL_PTREGS
regs->ax = sys_call_table[nr](regs);
#else
regs->ax = sys_call_table[nr](
regs->di, regs->si, regs->dx,
regs->r10, regs->r8, regs->r9);
#endif
}
syscall_return_slowpath(regs);
......
......@@ -7,14 +7,19 @@
#include <asm/asm-offsets.h>
#include <asm/syscall.h>
#ifdef CONFIG_SYSCALL_PTREGS
/* this is a lie, but it does not hurt as sys_ni_syscall just returns -EINVAL */
extern asmlinkage long sys_ni_syscall(const struct pt_regs *);
#define __SYSCALL_64(nr, sym, qual) extern asmlinkage long sym(const struct pt_regs *);
#else /* CONFIG_SYSCALL_PTREGS */
extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#define __SYSCALL_64(nr, sym, qual) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#endif /* CONFIG_SYSCALL_PTREGS */
#include <asm/syscalls_64.h>
#undef __SYSCALL_64
#define __SYSCALL_64(nr, sym, qual) [nr] = sym,
extern long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
asmlinkage const sys_call_ptr_t sys_call_table[__NR_syscall_max+1] = {
/*
* Smells like a compiler bug -- it doesn't work
......
......@@ -127,6 +127,9 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
int vsyscall_nr, syscall_nr, tmp;
int prev_sig_on_uaccess_err;
long ret;
#ifdef CONFIG_SYSCALL_PTREGS
unsigned long orig_dx;
#endif
/*
* No point in checking CS -- the only way to get here is a user mode
......@@ -227,19 +230,38 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
ret = -EFAULT;
switch (vsyscall_nr) {
case 0:
#ifdef CONFIG_SYSCALL_PTREGS
/* this decodes regs->di and regs->si on its own */
ret = sys_gettimeofday(regs);
#else
ret = sys_gettimeofday(
(struct timeval __user *)regs->di,
(struct timezone __user *)regs->si);
#endif /* CONFIG_SYSCALL_PTREGS */
break;
case 1:
#ifdef CONFIG_SYSCALL_PTREGS
/* this decodes regs->di on its own */
ret = sys_time(regs);
#else
ret = sys_time((time_t __user *)regs->di);
#endif /* CONFIG_SYSCALL_PTREGS */
break;
case 2:
#ifdef CONFIG_SYSCALL_PTREGS
/* while we could clobber regs->dx, we didn't in the past... */
orig_dx = regs->dx;
regs->dx = 0;
/* this decodes regs->di, regs->si and regs->dx on its own */
ret = sys_getcpu(regs);
regs->dx = orig_dx;
#else
ret = sys_getcpu((unsigned __user *)regs->di,
(unsigned __user *)regs->si,
NULL);
#endif /* CONFIG_SYSCALL_PTREGS */
break;
}
......
......@@ -20,9 +20,13 @@
#include <asm/thread_info.h> /* for TS_COMPAT */
#include <asm/unistd.h>
#ifdef CONFIG_SYSCALL_PTREGS
typedef asmlinkage long (*sys_call_ptr_t)(const struct pt_regs *);
#else
typedef asmlinkage long (*sys_call_ptr_t)(unsigned long, unsigned long,
unsigned long, unsigned long,
unsigned long, unsigned long);
#endif /* CONFIG_SYSCALL_PTREGS */
extern const sys_call_ptr_t sys_call_table[];
#if defined(CONFIG_X86_32)
......
/* SPDX-License-Identifier: GPL-2.0 */
/*
* syscall_wrapper.h - x86 specific wrappers to syscall definitions
*/
#ifndef _ASM_X86_SYSCALL_WRAPPER_H
#define _ASM_X86_SYSCALL_WRAPPER_H
/*
* Instead of the generic __SYSCALL_DEFINEx() definition, this macro takes
* struct pt_regs *regs as the only argument of the syscall stub named
* sys_*(). It decodes just the registers it needs and passes them on to
* the SyS_*() wrapper and then to the SYSC_*() function doing the actual job.
* These wrappers and functions are inlined, meaning that the assembly looks
* as follows (slightly re-ordered):
*
* <sys_recv>: <-- syscall with 4 parameters
* callq <__fentry__>
*
* mov 0x70(%rdi),%rdi <-- decode regs->di
* mov 0x68(%rdi),%rsi <-- decode regs->si
* mov 0x60(%rdi),%rdx <-- decode regs->dx
* mov 0x38(%rdi),%rcx <-- decode regs->r10
*
* xor %r9d,%r9d <-- clear %r9
* xor %r8d,%r8d <-- clear %r8
*
* callq __sys_recvfrom <-- do the actual work in __sys_recvfrom()
* which takes 6 arguments
*
* cltq <-- extend return value to 64-bit
* retq <-- return
*
* This approach avoids leaking random user-provided register content down
* the call chain.
*
* As the generic SYSCALL_DEFINE0() macro does not decode any parameters for
* obvious reasons, and passing struct pt_regs *regs to it in %rdi does not
* hurt, there is no need to override it.
*/
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long sys##name(const struct pt_regs *regs); \
ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
static long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
asmlinkage long sys##name(const struct pt_regs *regs) \
{ \
return SyS##name(__MAP(x,__SC_ARGS \
,,regs->di,,regs->si,,regs->dx \
,,regs->r10,,regs->r8,,regs->r9)); \
} \
static long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
__MAP(x,__SC_TEST,__VA_ARGS__); \
__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
return ret; \
} \
static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
/*
* For VSYSCALLS, we need to declare these three syscalls with the new
* pt_regs-based calling convention for in-kernel use.
*/
struct pt_regs;
asmlinkage long sys_getcpu(const struct pt_regs *regs); /* di,si,dx */
asmlinkage long sys_gettimeofday(const struct pt_regs *regs); /* di,si */
asmlinkage long sys_time(const struct pt_regs *regs); /* di */
#endif /* _ASM_X86_SYSCALL_WRAPPER_H */
......@@ -18,6 +18,12 @@
/* Common in X86_32 and X86_64 */
/* kernel/ioport.c */
long ksys_ioperm(unsigned long from, unsigned long num, int turn_on);
#ifndef CONFIG_SYSCALL_PTREGS
/*
* If CONFIG_SYSCALL_PTREGS is enabled, a different syscall calling convention
* is used. Do not include these -- invalid -- prototypes then
*/
asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
asmlinkage long sys_iopl(unsigned int);
......@@ -53,4 +59,5 @@ asmlinkage long sys_mmap(unsigned long, unsigned long, unsigned long,
unsigned long, unsigned long, unsigned long);
#endif /* CONFIG_X86_32 */
#endif /* CONFIG_SYSCALL_PTREGS */
#endif /* _ASM_X86_SYSCALLS_H */
......@@ -102,7 +102,7 @@ union bpf_attr;
* for SYSCALL_DEFINE<n>/COMPAT_SYSCALL_DEFINE<n>
*/
#define __MAP0(m,...)
#define __MAP1(m,t,a) m(t,a)
#define __MAP1(m,t,a,...) m(t,a)
#define __MAP2(m,t,a,...) m(t,a), __MAP1(m,__VA_ARGS__)
#define __MAP3(m,t,a,...) m(t,a), __MAP2(m,__VA_ARGS__)
#define __MAP4(m,t,a,...) m(t,a), __MAP3(m,__VA_ARGS__)
......
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