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syscalls/x86: Use 'struct pt_regs' based syscall calling convention f…
…or 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 <[email protected]>
| Signed-off-by: Linus Torvalds <[email protected]>
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 <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>- Loading branch information
Dominik Brodowski
authored and
Ingo Molnar
committed
Apr 5, 2018
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,70 @@ | ||
| /* 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 */ |
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