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Subject[PATCH v4 16/18] x86-32: Enable pt_regs based syscalls
Date
Enable pt_regs based syscalls for 32-bit.  This makes the 32-bit native
kernel consistent with the 64-bit kernel, and improves the syscall
interface by not needing to push all 6 potential arguments onto the stack.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
arch/x86/Kconfig | 2 +-
arch/x86/entry/common.c | 15 ----
arch/x86/entry/syscall_32.c | 15 +---
arch/x86/include/asm/syscall.h | 6 --
arch/x86/include/asm/syscall_wrapper.h | 111 ++++++++++++++-----------
arch/x86/include/asm/syscalls.h | 29 -------
6 files changed, 64 insertions(+), 114 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 532f52b99094..b65f07a06549 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -30,7 +30,6 @@ config X86_64
select MODULES_USE_ELF_RELA
select NEED_DMA_MAP_STATE
select SWIOTLB
- select ARCH_HAS_SYSCALL_WRAPPER

config FORCE_DYNAMIC_FTRACE
def_bool y
@@ -79,6 +78,7 @@ config X86
select ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_HAS_STRICT_MODULE_RWX
select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
+ select ARCH_HAS_SYSCALL_WRAPPER
select ARCH_HAS_UBSAN_SANITIZE_ALL
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index c3a8e6513f74..76735ec813e6 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -334,20 +334,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)

if (likely(nr < IA32_NR_syscalls)) {
nr = array_index_nospec(nr, IA32_NR_syscalls);
-#ifdef CONFIG_IA32_EMULATION
regs->ax = ia32_sys_call_table[nr](regs);
-#else
- /*
- * It's possible that a 32-bit syscall implementation
- * takes a 64-bit parameter but nonetheless assumes that
- * the high bits are zero. Make sure we zero-extend all
- * of the args.
- */
- regs->ax = ia32_sys_call_table[nr](
- (unsigned int)regs->bx, (unsigned int)regs->cx,
- (unsigned int)regs->dx, (unsigned int)regs->si,
- (unsigned int)regs->di, (unsigned int)regs->bp);
-#endif /* CONFIG_IA32_EMULATION */
}

syscall_return_slowpath(regs);
@@ -440,9 +427,7 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
}
#endif

-#ifdef CONFIG_X86_64
SYSCALL_DEFINE0(ni_syscall)
{
return -ENOSYS;
}
-#endif
diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
index 41ec9c66fe15..097413c705ad 100644
--- a/arch/x86/entry/syscall_32.c
+++ b/arch/x86/entry/syscall_32.c
@@ -4,33 +4,22 @@
#include <linux/linkage.h>
#include <linux/sys.h>
#include <linux/cache.h>
+#include <linux/syscalls.h>
#include <asm/unistd.h>
#include <asm/syscall.h>

-#ifdef CONFIG_IA32_EMULATION
-/* On X86_64, we use struct pt_regs * to pass parameters to syscalls */
#define __SYSCALL_I386(nr, sym) extern asmlinkage long __ia32_##sym(const struct pt_regs *);
-#define __sys_ni_syscall __ia32_sys_ni_syscall
-#else /* CONFIG_IA32_EMULATION */
-#define __SYSCALL_I386(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-#define __sys_ni_syscall sys_ni_syscall
-#endif /* CONFIG_IA32_EMULATION */

#include <asm/syscalls_32.h>
#undef __SYSCALL_I386

-#ifdef CONFIG_IA32_EMULATION
#define __SYSCALL_I386(nr, sym) [nr] = __ia32_##sym,
-#else /* CONFIG_IA32_EMULATION */
-#define __SYSCALL_I386(nr, sym) [nr] = sym,
-#endif /* CONFIG_IA32_EMULATION */

__visible const sys_call_ptr_t ia32_sys_call_table[__NR_ia32_syscall_max+1] = {
/*
* Smells like a compiler bug -- it doesn't work
* when the & below is removed.
*/
- [0 ... __NR_ia32_syscall_max] = &__sys_ni_syscall,
+ [0 ... __NR_ia32_syscall_max] = &__ia32_sys_ni_syscall,
#include <asm/syscalls_32.h>
};
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index f4d010d0fa30..bb427d8cb1ef 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -16,13 +16,7 @@
#include <asm/thread_info.h> /* for TS_COMPAT */
#include <asm/unistd.h>

-#ifdef CONFIG_X86_64
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_X86_64 */
extern const sys_call_ptr_t sys_call_table[];

#if defined(CONFIG_X86_32)
diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
index 0f126e40a464..5e13e2caf2e4 100644
--- a/arch/x86/include/asm/syscall_wrapper.h
+++ b/arch/x86/include/asm/syscall_wrapper.h
@@ -11,6 +11,47 @@ struct pt_regs;
extern asmlinkage long __x64_sys_ni_syscall(const struct pt_regs *regs);
extern asmlinkage long __ia32_sys_ni_syscall(const struct pt_regs *regs);

+/*
+ * Instead of the generic __SYSCALL_DEFINEx() definition, the x86 version takes
+ * struct pt_regs *regs as the only argument of the syscall stub(s) named as:
+ * __x64_sys_*() - 64-bit native syscall
+ * __ia32_sys_*() - 32-bit native syscall or common compat syscall
+ * __ia32_compat_sys_*() - 32-bit compat syscall
+ * __x32_compat_sys_*() - 64-bit X32 compat syscall
+ *
+ * The registers are decoded according to the ABI:
+ * 64-bit: RDI, RSI, RDX, R10, R8, R9
+ * 32-bit: EBX, ECX, EDX, ESI, EDI, EBP
+ *
+ * The stub then passes the decoded arguments to the __se_sys_*() wrapper to
+ * perform sign-extension (omitted for zero-argument syscalls). Finally the
+ * arguments are passed to the __do_sys_*() function which is the actual
+ * syscall. These wrappers are marked as inline so the compiler can optimize
+ * the functions where appropriate.
+ *
+ * Example assembly (slightly re-ordered for better readability):
+ *
+ * <__x64_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.
+ */
+
/* Mapping of registers to parameters for syscalls on x86-64 and x32 */
#define SC_X86_64_REGS_TO_ARGS(x, ...) \
__MAP(x,__SC_ARGS \
@@ -68,6 +109,26 @@ extern asmlinkage long __ia32_sys_ni_syscall(const struct pt_regs *regs);
#define __X64_SYS_NI(name)
#endif /* CONFIG_X86_64 */

+#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+#define __IA32_SYS_STUB0(name) \
+ __SYS_STUB0(ia32, sys_##name)
+
+#define __IA32_SYS_STUBx(x, name, ...) \
+ __SYS_STUBx(ia32, sys##name, \
+ SC_IA32_REGS_TO_ARGS(x, __VA_ARGS__))
+
+#define __IA32_COND_SYSCALL(name) \
+ __COND_SYSCALL(ia32, sys_##name)
+
+#define __IA32_SYS_NI(name) \
+ __SYS_NI(ia32, sys_##name)
+#else /* CONFIG_X86_32 || CONFIG_IA32_EMULATION */
+#define __IA32_SYS_STUB0(name)
+#define __IA32_SYS_STUBx(x, name, ...)
+#define __IA32_COND_SYSCALL(name)
+#define __IA32_SYS_NI(name)
+#endif /* CONFIG_X86_32 || CONFIG_IA32_EMULATION */
+
#ifdef CONFIG_IA32_EMULATION
/*
* For IA32 emulation, we need to handle "compat" syscalls *and* create
@@ -90,27 +151,11 @@ extern asmlinkage long __ia32_sys_ni_syscall(const struct pt_regs *regs);
#define __IA32_COMPAT_SYS_NI(name) \
__SYS_NI(ia32, compat_sys_##name)

-#define __IA32_SYS_STUB0(name) \
- __SYS_STUB0(ia32, sys_##name)
-
-#define __IA32_SYS_STUBx(x, name, ...) \
- __SYS_STUBx(ia32, sys##name, \
- SC_IA32_REGS_TO_ARGS(x, __VA_ARGS__))
-
-#define __IA32_COND_SYSCALL(name) \
- __COND_SYSCALL(ia32, sys_##name)
-
-#define __IA32_SYS_NI(name) \
- __SYS_NI(ia32, sys_##name)
#else /* CONFIG_IA32_EMULATION */
#define __IA32_COMPAT_SYS_STUB0(name)
#define __IA32_COMPAT_SYS_STUBx(x, name, ...)
#define __IA32_COMPAT_COND_SYSCALL(name)
#define __IA32_COMPAT_SYS_NI(name)
-#define __IA32_SYS_STUB0(name)
-#define __IA32_SYS_STUBx(x, name, ...)
-#define __IA32_COND_SYSCALL(name)
-#define __IA32_SYS_NI(name)
#endif /* CONFIG_IA32_EMULATION */


@@ -180,40 +225,6 @@ extern asmlinkage long __ia32_sys_ni_syscall(const struct pt_regs *regs);

#endif /* CONFIG_COMPAT */

-
-/*
- * Instead of the generic __SYSCALL_DEFINEx() definition, this macro takes
- * struct pt_regs *regs as the only argument of the syscall stub named
- * __x64_sys_*(). It decodes just the registers it needs and passes them on to
- * the __se_sys_*() wrapper performing sign extension and then to the
- * __do_sys_*() function doing the actual job. These wrappers and functions
- * are inlined (at least in very most cases), meaning that the assembly looks
- * as follows (slightly re-ordered for better readability):
- *
- * <__x64_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.
- *
- * If IA32_EMULATION is enabled, this macro generates an additional wrapper
- * named __ia32_sys_*() which decodes the struct pt_regs *regs according
- * to the i386 calling convention (bx, cx, dx, si, di, bp).
- */
#define __SYSCALL_DEFINEx(x, name, ...) \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
index 91b7b6e1a115..06cbdca634d6 100644
--- a/arch/x86/include/asm/syscalls.h
+++ b/arch/x86/include/asm/syscalls.h
@@ -17,33 +17,4 @@
/* kernel/ioport.c */
long ksys_ioperm(unsigned long from, unsigned long num, int turn_on);

-#ifdef CONFIG_X86_32
-/*
- * These definitions are only valid on pure 32-bit systems; x86-64 uses a
- * different syscall calling convention
- */
-asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
-asmlinkage long sys_iopl(unsigned int);
-
-/* kernel/ldt.c */
-asmlinkage long sys_modify_ldt(int, void __user *, unsigned long);
-
-/* kernel/signal.c */
-asmlinkage long sys_rt_sigreturn(void);
-
-/* kernel/tls.c */
-asmlinkage long sys_set_thread_area(struct user_desc __user *);
-asmlinkage long sys_get_thread_area(struct user_desc __user *);
-
-/* X86_32 only */
-
-/* kernel/signal.c */
-asmlinkage long sys_sigreturn(void);
-
-/* kernel/vm86_32.c */
-struct vm86_struct;
-asmlinkage long sys_vm86old(struct vm86_struct __user *);
-asmlinkage long sys_vm86(unsigned long, unsigned long);
-
-#endif /* CONFIG_X86_32 */
#endif /* _ASM_X86_SYSCALLS_H */
--
2.24.1
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