This is a note to let you know that I've just added the patch titled
x86/entry: Convert INT 0x80 emulation to IDTENTRY
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-entry-convert-int-0x80-emulation-to-idtentry.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 65ab275c18d075f9ffc82df7508fbdf9a69b1d8b Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Mon, 4 Dec 2023 11:31:39 +0300
Subject: x86/entry: Convert INT 0x80 emulation to IDTENTRY
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[ upstream commit be5341eb0d43b1e754799498bd2e8756cc167a41 ]
There is no real reason to have a separate ASM entry point implementation
for the legacy INT 0x80 syscall emulation on 64-bit.
IDTENTRY provides all the functionality needed with the only difference
that it does not:
- save the syscall number (AX) into pt_regs::orig_ax
- set pt_regs::ax to -ENOSYS
Both can be done safely in the C code of an IDTENTRY before invoking any of
the syscall related functions which depend on this convention.
Aside of ASM code reduction this prepares for detecting and handling a
local APIC injected vector 0x80.
[ kirill.shutemov: More verbose comments ]
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v6.0+
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/common.c | 58 ++++++++++++++++++++++++++++-
arch/x86/entry/entry_64_compat.S | 77 ---------------------------------------
arch/x86/include/asm/idtentry.h | 4 ++
arch/x86/include/asm/proto.h | 4 --
arch/x86/kernel/idt.c | 2 -
arch/x86/xen/enlighten_pv.c | 2 -
arch/x86/xen/xen-asm.S | 2 -
7 files changed, 64 insertions(+), 85 deletions(-)
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -119,7 +119,62 @@ static __always_inline void do_syscall_3
}
}
-/* Handles int $0x80 */
+#ifdef CONFIG_IA32_EMULATION
+/**
+ * int80_emulation - 32-bit legacy syscall entry
+ *
+ * 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
+ */
+DEFINE_IDTENTRY_RAW(int80_emulation)
+{
+ int nr;
+
+ /* Establish kernel context. */
+ enter_from_user_mode(regs);
+
+ instrumentation_begin();
+ add_random_kstack_offset();
+
+ /*
+ * 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);
+}
+#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);
@@ -138,6 +193,7 @@ __visible noinstr void do_int80_syscall_
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
+#endif /* !CONFIG_IA32_EMULATION */
static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
{
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -277,80 +277,3 @@ SYM_INNER_LABEL(entry_SYSRETL_compat_end
ANNOTATE_NOENDBR
int3
SYM_CODE_END(entry_SYSCALL_compat)
-
-/*
- * 32-bit legacy system call entry.
- *
- * 32-bit x86 Linux system calls traditionally used the INT $0x80
- * instruction. INT $0x80 lands here.
- *
- * 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
- * $0x80 regardless of what instruction was originally used to do the
- * system call.
- *
- * This is considered a slow path. It is not used by most libc
- * implementations on modern hardware except during process startup.
- *
- * Arguments:
- * eax system call number
- * ebx arg1
- * ecx arg2
- * edx arg3
- * esi arg4
- * edi arg5
- * ebp arg6
- */
-SYM_CODE_START(entry_INT80_compat)
- UNWIND_HINT_ENTRY
- ENDBR
- /*
- * Interrupts are off on entry.
- */
- ASM_CLAC /* Do this early to minimize exposure */
- ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
-
- /*
- * User tracing code (ptrace or signal handlers) might assume that
- * the saved RAX contains a 32-bit number when we're invoking a 32-bit
- * syscall. Just in case the high bits are nonzero, zero-extend
- * the syscall number. (This could almost certainly be deleted
- * with no ill effects.)
- */
- movl %eax, %eax
-
- /* switch to thread stack expects orig_ax and rdi to be pushed */
- pushq %rax /* pt_regs->orig_ax */
-
- /* Need to switch before accessing the thread stack. */
- SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
-
- /* In the Xen PV case we already run on the thread stack. */
- ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
-
- movq %rsp, %rax
- movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
-
- pushq 5*8(%rax) /* regs->ss */
- pushq 4*8(%rax) /* regs->rsp */
- pushq 3*8(%rax) /* regs->eflags */
- pushq 2*8(%rax) /* regs->cs */
- pushq 1*8(%rax) /* regs->ip */
- pushq 0*8(%rax) /* regs->orig_ax */
-.Lint80_keep_stack:
-
- PUSH_AND_CLEAR_REGS rax=$-ENOSYS
- UNWIND_HINT_REGS
-
- cld
-
- IBRS_ENTER
- UNTRAIN_RET
-
- movq %rsp, %rdi
- call do_int80_syscall_32
- jmp swapgs_restore_regs_and_return_to_usermode
-SYM_CODE_END(entry_INT80_compat)
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -569,6 +569,10 @@ DECLARE_IDTENTRY_RAW(X86_TRAP_UD, exc_i
DECLARE_IDTENTRY_RAW(X86_TRAP_BP, exc_int3);
DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_PF, exc_page_fault);
+#if defined(CONFIG_IA32_EMULATION)
+DECLARE_IDTENTRY_RAW(IA32_SYSCALL_VECTOR, int80_emulation);
+#endif
+
#ifdef CONFIG_X86_MCE
#ifdef CONFIG_X86_64
DECLARE_IDTENTRY_MCE(X86_TRAP_MC, exc_machine_check);
--- a/arch/x86/include/asm/proto.h
+++ b/arch/x86/include/asm/proto.h
@@ -32,10 +32,6 @@ void entry_SYSCALL_compat(void);
void entry_SYSCALL_compat_safe_stack(void);
void entry_SYSRETL_compat_unsafe_stack(void);
void entry_SYSRETL_compat_end(void);
-void entry_INT80_compat(void);
-#ifdef CONFIG_XEN_PV
-void xen_entry_INT80_compat(void);
-#endif
#endif
void x86_configure_nx(void);
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -117,7 +117,7 @@ static const __initconst struct idt_data
SYSG(X86_TRAP_OF, asm_exc_overflow),
#if defined(CONFIG_IA32_EMULATION)
- SYSG(IA32_SYSCALL_VECTOR, entry_INT80_compat),
+ SYSG(IA32_SYSCALL_VECTOR, asm_int80_emulation),
#elif defined(CONFIG_X86_32)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32),
#endif
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -623,7 +623,7 @@ static struct trap_array_entry trap_arra
TRAP_ENTRY(exc_int3, false ),
TRAP_ENTRY(exc_overflow, false ),
#ifdef CONFIG_IA32_EMULATION
- { entry_INT80_compat, xen_entry_INT80_compat, false },
+ TRAP_ENTRY(int80_emulation, false ),
#endif
TRAP_ENTRY(exc_page_fault, false ),
TRAP_ENTRY(exc_divide_error, false ),
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -156,7 +156,7 @@ xen_pv_trap asm_xenpv_exc_machine_check
#endif /* CONFIG_X86_MCE */
xen_pv_trap asm_exc_simd_coprocessor_error
#ifdef CONFIG_IA32_EMULATION
-xen_pv_trap entry_INT80_compat
+xen_pv_trap asm_int80_emulation
#endif
xen_pv_trap asm_exc_xen_unknown_trap
xen_pv_trap asm_exc_xen_hypervisor_callback
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-6.1/x86-entry-convert-int-0x80-emulation-to-idtentry.patch
queue-6.1/x86-coco-disable-32-bit-emulation-by-default-on-tdx-and-sev.patch
queue-6.1/x86-introduce-ia32_enabled.patch
queue-6.1/x86-acpi-ignore-invalid-x2apic-entries.patch
queue-6.1/x86-entry-do-not-allow-external-0x80-interrupts.patch
queue-6.1/x86-tdx-allow-32-bit-emulation-by-default.patch
queue-6.1/hrtimers-push-pending-hrtimers-away-from-outgoing-cp.patch
