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x86/syscall/32: Move 32-bit syscall dispatch code

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Move the 32-bit syscall dispatch code to syscall_32.c.

No functional changes.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250314151220.862768-3-brgerst@gmail.com
This commit is contained in:
Brian Gerst
2025-03-14 11:12:15 -04:00
committed by Ingo Molnar
parent 1ab7b5ed44
commit b634b02e2b
3 changed files with 329 additions and 323 deletions
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2
arch/x86/entry/Makefile
View File

@@ -8,8 +8,10 @@ UBSAN_SANITIZE := n
KCOV_INSTRUMENT := n
CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE)
CFLAGS_common.o += -fno-stack-protector
CFLAGS_syscall_32.o += -fno-stack-protector
obj-y := entry.o entry_$(BITS).o syscall_$(BITS).o
obj-y += common.o

321
arch/x86/entry/common.c
View File

@@ -125,327 +125,6 @@ __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
}
#endif
#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
static __always_inline int syscall_32_enter(struct pt_regs *regs)
{
if (IS_ENABLED(CONFIG_IA32_EMULATION))
current_thread_info()->status |= TS_COMPAT;
return (int)regs->orig_ax;
}
#ifdef CONFIG_IA32_EMULATION
bool __ia32_enabled __ro_after_init = !IS_ENABLED(CONFIG_IA32_EMULATION_DEFAULT_DISABLED);
static int __init ia32_emulation_override_cmdline(char *arg)
{
return kstrtobool(arg, &__ia32_enabled);
}
early_param("ia32_emulation", ia32_emulation_override_cmdline);
#endif
/*
* Invoke a 32-bit syscall. Called with IRQs on in CT_STATE_KERNEL.
*/
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
{
/*
* Convert negative numbers to very high and thus out of range
* numbers for comparisons.
*/
unsigned int unr = nr;
if (likely(unr < IA32_NR_syscalls)) {
unr = array_index_nospec(unr, IA32_NR_syscalls);
regs->ax = ia32_sys_call(regs, unr);
} else if (nr != -1) {
regs->ax = __ia32_sys_ni_syscall(regs);
}
}
#ifdef CONFIG_IA32_EMULATION
static __always_inline bool int80_is_external(void)
{
const unsigned int offs = (0x80 / 32) * 0x10;
const u32 bit = BIT(0x80 % 32);
/* The local APIC on XENPV guests is fake */
if (cpu_feature_enabled(X86_FEATURE_XENPV))
return false;
/*
* If vector 0x80 is set in the APIC ISR then this is an external
* interrupt. Either from broken hardware or injected by a VMM.
*
* Note: In guest mode this is only valid for secure guests where
* the secure module fully controls the vAPIC exposed to the guest.
*/
return apic_read(APIC_ISR + offs) & bit;
}
/**
* do_int80_emulation - 32-bit legacy syscall C entry from asm
* @regs: syscall arguments in struct pt_args on the stack.
*
* This entry point can be used by 32-bit and 64-bit programs to perform
* 32-bit system calls. Instances of INT $0x80 can be found inline in
* various programs and libraries. It is also used by the vDSO's
* __kernel_vsyscall fallback for hardware that doesn't support a faster
* entry method. Restarted 32-bit system calls also fall back to INT
* $0x80 regardless of what instruction was originally used to do the
* system call.
*
* This is considered a slow path. It is not used by most libc
* implementations on modern hardware except during process startup.
*
* The arguments for the INT $0x80 based syscall are on stack in the
* pt_regs structure:
* eax: system call number
* ebx, ecx, edx, esi, edi, ebp: arg1 - arg 6
*/
__visible noinstr void do_int80_emulation(struct pt_regs *regs)
{
int nr;
/* Kernel does not use INT $0x80! */
if (unlikely(!user_mode(regs))) {
irqentry_enter(regs);
instrumentation_begin();
panic("Unexpected external interrupt 0x80\n");
}
/*
* Establish kernel context for instrumentation, including for
* int80_is_external() below which calls into the APIC driver.
* Identical for soft and external interrupts.
*/
enter_from_user_mode(regs);
instrumentation_begin();
add_random_kstack_offset();
/* Validate that this is a soft interrupt to the extent possible */
if (unlikely(int80_is_external()))
panic("Unexpected external interrupt 0x80\n");
/*
* The low level idtentry code pushed -1 into regs::orig_ax
* and regs::ax contains the syscall number.
*
* User tracing code (ptrace or signal handlers) might assume
* that the regs::orig_ax contains a 32-bit number on invoking
* a 32-bit syscall.
*
* Establish the syscall convention by saving the 32bit truncated
* syscall number in regs::orig_ax and by invalidating regs::ax.
*/
regs->orig_ax = regs->ax & GENMASK(31, 0);
regs->ax = -ENOSYS;
nr = syscall_32_enter(regs);
local_irq_enable();
nr = syscall_enter_from_user_mode_work(regs, nr);
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#ifdef CONFIG_X86_FRED
/*
* A FRED-specific INT80 handler is warranted for the follwing reasons:
*
* 1) As INT instructions and hardware interrupts are separate event
* types, FRED does not preclude the use of vector 0x80 for external
* interrupts. As a result, the FRED setup code does not reserve
* vector 0x80 and calling int80_is_external() is not merely
* suboptimal but actively incorrect: it could cause a system call
* to be incorrectly ignored.
*
* 2) It is called only for handling vector 0x80 of event type
* EVENT_TYPE_SWINT and will never be called to handle any external
* interrupt (event type EVENT_TYPE_EXTINT).
*
* 3) FRED has separate entry flows depending on if the event came from
* user space or kernel space, and because the kernel does not use
* INT insns, the FRED kernel entry handler fred_entry_from_kernel()
* falls through to fred_bad_type() if the event type is
* EVENT_TYPE_SWINT, i.e., INT insns. So if the kernel is handling
* an INT insn, it can only be from a user level.
*
* 4) int80_emulation() does a CLEAR_BRANCH_HISTORY. While FRED will
* likely take a different approach if it is ever needed: it
* probably belongs in either fred_intx()/ fred_other() or
* asm_fred_entrypoint_user(), depending on if this ought to be done
* for all entries from userspace or only system
* calls.
*
* 5) INT $0x80 is the fast path for 32-bit system calls under FRED.
*/
DEFINE_FREDENTRY_RAW(int80_emulation)
{
int nr;
enter_from_user_mode(regs);
instrumentation_begin();
add_random_kstack_offset();
/*
* FRED pushed 0 into regs::orig_ax and regs::ax contains the
* syscall number.
*
* User tracing code (ptrace or signal handlers) might assume
* that the regs::orig_ax contains a 32-bit number on invoking
* a 32-bit syscall.
*
* Establish the syscall convention by saving the 32bit truncated
* syscall number in regs::orig_ax and by invalidating regs::ax.
*/
regs->orig_ax = regs->ax & GENMASK(31, 0);
regs->ax = -ENOSYS;
nr = syscall_32_enter(regs);
local_irq_enable();
nr = syscall_enter_from_user_mode_work(regs, nr);
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#endif
#else /* CONFIG_IA32_EMULATION */
/* Handles int $0x80 on a 32bit kernel */
__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
{
int nr = syscall_32_enter(regs);
add_random_kstack_offset();
/*
* Subtlety here: if ptrace pokes something larger than 2^31-1 into
* orig_ax, the int return value truncates it. This matches
* the semantics of syscall_get_nr().
*/
nr = syscall_enter_from_user_mode(regs, nr);
instrumentation_begin();
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#endif /* !CONFIG_IA32_EMULATION */
static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
{
int nr = syscall_32_enter(regs);
int res;
add_random_kstack_offset();
/*
* This cannot use syscall_enter_from_user_mode() as it has to
* fetch EBP before invoking any of the syscall entry work
* functions.
*/
syscall_enter_from_user_mode_prepare(regs);
instrumentation_begin();
/* Fetch EBP from where the vDSO stashed it. */
if (IS_ENABLED(CONFIG_X86_64)) {
/*
* Micro-optimization: the pointer we're following is
* explicitly 32 bits, so it can't be out of range.
*/
res = __get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp);
} else {
res = get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp);
}
if (res) {
/* User code screwed up. */
regs->ax = -EFAULT;
local_irq_disable();
instrumentation_end();
irqentry_exit_to_user_mode(regs);
return false;
}
nr = syscall_enter_from_user_mode_work(regs, nr);
/* Now this is just like a normal syscall. */
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
return true;
}
/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
__visible noinstr bool do_fast_syscall_32(struct pt_regs *regs)
{
/*
* Called using the internal vDSO SYSENTER/SYSCALL32 calling
* convention. Adjust regs so it looks like we entered using int80.
*/
unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
vdso_image_32.sym_int80_landing_pad;
/*
* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
* Fix it up.
*/
regs->ip = landing_pad;
/* Invoke the syscall. If it failed, keep it simple: use IRET. */
if (!__do_fast_syscall_32(regs))
return false;
/*
* Check that the register state is valid for using SYSRETL/SYSEXIT
* to exit to userspace. Otherwise use the slower but fully capable
* IRET exit path.
*/
/* XEN PV guests always use the IRET path */
if (cpu_feature_enabled(X86_FEATURE_XENPV))
return false;
/* EIP must point to the VDSO landing pad */
if (unlikely(regs->ip != landing_pad))
return false;
/* CS and SS must match the values set in MSR_STAR */
if (unlikely(regs->cs != __USER32_CS || regs->ss != __USER_DS))
return false;
/* If the TF, RF, or VM flags are set, use IRET */
if (unlikely(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)))
return false;
/* Use SYSRETL/SYSEXIT to exit to userspace */
return true;
}
/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
__visible noinstr bool do_SYSENTER_32(struct pt_regs *regs)
{
/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
regs->sp = regs->bp;
/* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
regs->flags |= X86_EFLAGS_IF;
return do_fast_syscall_32(regs);
}
#endif
SYSCALL_DEFINE0(ni_syscall)
{
return -ENOSYS;

329
arch/x86/entry/syscall_32.c
View File

@@ -1,10 +1,16 @@
// SPDX-License-Identifier: GPL-2.0
/* System call table for i386. */
// SPDX-License-Identifier: GPL-2.0-only
/* 32-bit system call dispatch */
#include <linux/linkage.h>
#include <linux/sys.h>
#include <linux/cache.h>
#include <linux/syscalls.h>
#include <linux/entry-common.h>
#include <linux/nospec.h>
#include <linux/uaccess.h>
#include <asm/apic.h>
#include <asm/traps.h>
#include <asm/cpufeature.h>
#include <asm/syscall.h>
#ifdef CONFIG_IA32_EMULATION
@@ -42,3 +48,322 @@ long ia32_sys_call(const struct pt_regs *regs, unsigned int nr)
default: return __ia32_sys_ni_syscall(regs);
}
};
static __always_inline int syscall_32_enter(struct pt_regs *regs)
{
if (IS_ENABLED(CONFIG_IA32_EMULATION))
current_thread_info()->status |= TS_COMPAT;
return (int)regs->orig_ax;
}
#ifdef CONFIG_IA32_EMULATION
bool __ia32_enabled __ro_after_init = !IS_ENABLED(CONFIG_IA32_EMULATION_DEFAULT_DISABLED);
static int __init ia32_emulation_override_cmdline(char *arg)
{
return kstrtobool(arg, &__ia32_enabled);
}
early_param("ia32_emulation", ia32_emulation_override_cmdline);
#endif
/*
* Invoke a 32-bit syscall. Called with IRQs on in CT_STATE_KERNEL.
*/
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
{
/*
* Convert negative numbers to very high and thus out of range
* numbers for comparisons.
*/
unsigned int unr = nr;
if (likely(unr < IA32_NR_syscalls)) {
unr = array_index_nospec(unr, IA32_NR_syscalls);
regs->ax = ia32_sys_call(regs, unr);
} else if (nr != -1) {
regs->ax = __ia32_sys_ni_syscall(regs);
}
}
#ifdef CONFIG_IA32_EMULATION
static __always_inline bool int80_is_external(void)
{
const unsigned int offs = (0x80 / 32) * 0x10;
const u32 bit = BIT(0x80 % 32);
/* The local APIC on XENPV guests is fake */
if (cpu_feature_enabled(X86_FEATURE_XENPV))
return false;
/*
* If vector 0x80 is set in the APIC ISR then this is an external
* interrupt. Either from broken hardware or injected by a VMM.
*
* Note: In guest mode this is only valid for secure guests where
* the secure module fully controls the vAPIC exposed to the guest.
*/
return apic_read(APIC_ISR + offs) & bit;
}
/**
* do_int80_emulation - 32-bit legacy syscall C entry from asm
* @regs: syscall arguments in struct pt_args on the stack.
*
* This entry point can be used by 32-bit and 64-bit programs to perform
* 32-bit system calls. Instances of INT $0x80 can be found inline in
* various programs and libraries. It is also used by the vDSO's
* __kernel_vsyscall fallback for hardware that doesn't support a faster
* entry method. Restarted 32-bit system calls also fall back to INT
* $0x80 regardless of what instruction was originally used to do the
* system call.
*
* This is considered a slow path. It is not used by most libc
* implementations on modern hardware except during process startup.
*
* The arguments for the INT $0x80 based syscall are on stack in the
* pt_regs structure:
* eax: system call number
* ebx, ecx, edx, esi, edi, ebp: arg1 - arg 6
*/
__visible noinstr void do_int80_emulation(struct pt_regs *regs)
{
int nr;
/* Kernel does not use INT $0x80! */
if (unlikely(!user_mode(regs))) {
irqentry_enter(regs);
instrumentation_begin();
panic("Unexpected external interrupt 0x80\n");
}
/*
* Establish kernel context for instrumentation, including for
* int80_is_external() below which calls into the APIC driver.
* Identical for soft and external interrupts.
*/
enter_from_user_mode(regs);
instrumentation_begin();
add_random_kstack_offset();
/* Validate that this is a soft interrupt to the extent possible */
if (unlikely(int80_is_external()))
panic("Unexpected external interrupt 0x80\n");
/*
* The low level idtentry code pushed -1 into regs::orig_ax
* and regs::ax contains the syscall number.
*
* User tracing code (ptrace or signal handlers) might assume
* that the regs::orig_ax contains a 32-bit number on invoking
* a 32-bit syscall.
*
* Establish the syscall convention by saving the 32bit truncated
* syscall number in regs::orig_ax and by invalidating regs::ax.
*/
regs->orig_ax = regs->ax & GENMASK(31, 0);
regs->ax = -ENOSYS;
nr = syscall_32_enter(regs);
local_irq_enable();
nr = syscall_enter_from_user_mode_work(regs, nr);
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#ifdef CONFIG_X86_FRED
/*
* A FRED-specific INT80 handler is warranted for the follwing reasons:
*
* 1) As INT instructions and hardware interrupts are separate event
* types, FRED does not preclude the use of vector 0x80 for external
* interrupts. As a result, the FRED setup code does not reserve
* vector 0x80 and calling int80_is_external() is not merely
* suboptimal but actively incorrect: it could cause a system call
* to be incorrectly ignored.
*
* 2) It is called only for handling vector 0x80 of event type
* EVENT_TYPE_SWINT and will never be called to handle any external
* interrupt (event type EVENT_TYPE_EXTINT).
*
* 3) FRED has separate entry flows depending on if the event came from
* user space or kernel space, and because the kernel does not use
* INT insns, the FRED kernel entry handler fred_entry_from_kernel()
* falls through to fred_bad_type() if the event type is
* EVENT_TYPE_SWINT, i.e., INT insns. So if the kernel is handling
* an INT insn, it can only be from a user level.
*
* 4) int80_emulation() does a CLEAR_BRANCH_HISTORY. While FRED will
* likely take a different approach if it is ever needed: it
* probably belongs in either fred_intx()/ fred_other() or
* asm_fred_entrypoint_user(), depending on if this ought to be done
* for all entries from userspace or only system
* calls.
*
* 5) INT $0x80 is the fast path for 32-bit system calls under FRED.
*/
DEFINE_FREDENTRY_RAW(int80_emulation)
{
int nr;
enter_from_user_mode(regs);
instrumentation_begin();
add_random_kstack_offset();
/*
* FRED pushed 0 into regs::orig_ax and regs::ax contains the
* syscall number.
*
* User tracing code (ptrace or signal handlers) might assume
* that the regs::orig_ax contains a 32-bit number on invoking
* a 32-bit syscall.
*
* Establish the syscall convention by saving the 32bit truncated
* syscall number in regs::orig_ax and by invalidating regs::ax.
*/
regs->orig_ax = regs->ax & GENMASK(31, 0);
regs->ax = -ENOSYS;
nr = syscall_32_enter(regs);
local_irq_enable();
nr = syscall_enter_from_user_mode_work(regs, nr);
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#endif
#else /* CONFIG_IA32_EMULATION */
/* Handles int $0x80 on a 32bit kernel */
__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
{
int nr = syscall_32_enter(regs);
add_random_kstack_offset();
/*
* Subtlety here: if ptrace pokes something larger than 2^31-1 into
* orig_ax, the int return value truncates it. This matches
* the semantics of syscall_get_nr().
*/
nr = syscall_enter_from_user_mode(regs, nr);
instrumentation_begin();
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
#endif /* !CONFIG_IA32_EMULATION */
static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
{
int nr = syscall_32_enter(regs);
int res;
add_random_kstack_offset();
/*
* This cannot use syscall_enter_from_user_mode() as it has to
* fetch EBP before invoking any of the syscall entry work
* functions.
*/
syscall_enter_from_user_mode_prepare(regs);
instrumentation_begin();
/* Fetch EBP from where the vDSO stashed it. */
if (IS_ENABLED(CONFIG_X86_64)) {
/*
* Micro-optimization: the pointer we're following is
* explicitly 32 bits, so it can't be out of range.
*/
res = __get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp);
} else {
res = get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp);
}
if (res) {
/* User code screwed up. */
regs->ax = -EFAULT;
local_irq_disable();
instrumentation_end();
irqentry_exit_to_user_mode(regs);
return false;
}
nr = syscall_enter_from_user_mode_work(regs, nr);
/* Now this is just like a normal syscall. */
do_syscall_32_irqs_on(regs, nr);
instrumentation_end();
syscall_exit_to_user_mode(regs);
return true;
}
/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
__visible noinstr bool do_fast_syscall_32(struct pt_regs *regs)
{
/*
* Called using the internal vDSO SYSENTER/SYSCALL32 calling
* convention. Adjust regs so it looks like we entered using int80.
*/
unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
vdso_image_32.sym_int80_landing_pad;
/*
* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
* Fix it up.
*/
regs->ip = landing_pad;
/* Invoke the syscall. If it failed, keep it simple: use IRET. */
if (!__do_fast_syscall_32(regs))
return false;
/*
* Check that the register state is valid for using SYSRETL/SYSEXIT
* to exit to userspace. Otherwise use the slower but fully capable
* IRET exit path.
*/
/* XEN PV guests always use the IRET path */
if (cpu_feature_enabled(X86_FEATURE_XENPV))
return false;
/* EIP must point to the VDSO landing pad */
if (unlikely(regs->ip != landing_pad))
return false;
/* CS and SS must match the values set in MSR_STAR */
if (unlikely(regs->cs != __USER32_CS || regs->ss != __USER_DS))
return false;
/* If the TF, RF, or VM flags are set, use IRET */
if (unlikely(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)))
return false;
/* Use SYSRETL/SYSEXIT to exit to userspace */
return true;
}
/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
__visible noinstr bool do_SYSENTER_32(struct pt_regs *regs)
{
/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
regs->sp = regs->bp;
/* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
regs->flags |= X86_EFLAGS_IF;
return do_fast_syscall_32(regs);
}