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fa697140f9
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: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Linus 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.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
71 lines
2.5 KiB
C
71 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* syscall_wrapper.h - x86 specific wrappers to syscall definitions
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*/
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#ifndef _ASM_X86_SYSCALL_WRAPPER_H
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#define _ASM_X86_SYSCALL_WRAPPER_H
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/*
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* Instead of the generic __SYSCALL_DEFINEx() definition, this macro takes
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* struct pt_regs *regs as the only argument of the syscall stub named
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* sys_*(). It decodes just the registers it needs and passes them on to
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* the SyS_*() wrapper and then to the SYSC_*() function doing the actual job.
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* These wrappers and functions are inlined, meaning that the assembly looks
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* as follows (slightly re-ordered):
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*
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* <sys_recv>: <-- syscall with 4 parameters
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* callq <__fentry__>
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*
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* mov 0x70(%rdi),%rdi <-- decode regs->di
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* mov 0x68(%rdi),%rsi <-- decode regs->si
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* mov 0x60(%rdi),%rdx <-- decode regs->dx
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* mov 0x38(%rdi),%rcx <-- decode regs->r10
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*
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* xor %r9d,%r9d <-- clear %r9
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* xor %r8d,%r8d <-- clear %r8
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*
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* callq __sys_recvfrom <-- do the actual work in __sys_recvfrom()
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* which takes 6 arguments
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*
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* cltq <-- extend return value to 64-bit
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* retq <-- return
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*
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* This approach avoids leaking random user-provided register content down
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* the call chain.
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*
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* As the generic SYSCALL_DEFINE0() macro does not decode any parameters for
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* obvious reasons, and passing struct pt_regs *regs to it in %rdi does not
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* hurt, there is no need to override it.
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*/
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#define __SYSCALL_DEFINEx(x, name, ...) \
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asmlinkage long sys##name(const struct pt_regs *regs); \
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ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
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static long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
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static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
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asmlinkage long sys##name(const struct pt_regs *regs) \
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{ \
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return SyS##name(__MAP(x,__SC_ARGS \
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,,regs->di,,regs->si,,regs->dx \
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,,regs->r10,,regs->r8,,regs->r9)); \
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} \
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static long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
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{ \
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long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
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__MAP(x,__SC_TEST,__VA_ARGS__); \
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__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
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return ret; \
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} \
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static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
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/*
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* For VSYSCALLS, we need to declare these three syscalls with the new
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* pt_regs-based calling convention for in-kernel use.
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*/
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struct pt_regs;
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asmlinkage long sys_getcpu(const struct pt_regs *regs); /* di,si,dx */
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asmlinkage long sys_gettimeofday(const struct pt_regs *regs); /* di,si */
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asmlinkage long sys_time(const struct pt_regs *regs); /* di */
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#endif /* _ASM_X86_SYSCALL_WRAPPER_H */
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