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@@ -0,0 +1,70 @@
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+/* 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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+
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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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+/*
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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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+/*
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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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+
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+#endif /* _ASM_X86_SYSCALL_WRAPPER_H */
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Dominik Brodowski