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entry: disable interrupts during usermode transition #316

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merged 2 commits into from
Nov 7, 2023
Merged

entry: disable interrupts during usermode transition #316

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badd4cb
entry: disable interrupts during usermode transition
wipawel Nov 3, 2023
7340142
arch,entry: restore default GS (PERCPU) segment selector
wipawel Nov 6, 2023
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11 changes: 9 additions & 2 deletions arch/x86/entry.S
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,10 @@ ENTRY(syscall_exit)
SWITCH_STACK
POPF

/* Restore default GS (PERCPU) segment selector */
mov $__KERN_PERCPU, %_ASM_AX
mov %_ASM_AX, %gs

/* Save exit code to return value register (AX) */
mov %_ASM_SI, cpu_regs_ax(%_ASM_SP)
RESTORE_ALL_REGS
Expand All @@ -196,6 +200,9 @@ ENTRY(enter_usermode)
SAVE_ALL_REGS
PUSHF

/* Disable interrupts for stack switch and swapgs */
cli

/* Save user stack pointer onto per-cpu */
mov %_ASM_DX, %gs:(usermode_private)

Expand All @@ -208,8 +215,8 @@ ENTRY(enter_usermode)

/* EFLAGS */
PUSHF

orl $X86_EFLAGS_IOPL, (%_ASM_SP)
/* Set IOPL=3 and re-enable interrupts via IRET */
orl $(X86_EFLAGS_IOPL | X86_EFLAGS_IF), (%_ASM_SP)

/* CS + IP */
push $__USER_CS
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2 changes: 1 addition & 1 deletion arch/x86/traps.c
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Expand Up @@ -114,7 +114,7 @@ static void init_gdt(percpu_t *percpu) {
lgdt(&percpu->gdt_ptr);

write_ss(__KERN_DS);
write_gs(GDT_PERCPU << 3);
write_gs(__KERN_PERCPU);
wrmsr(MSR_KERNEL_GS_BASE, 0x0);

init_tss(percpu);
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2 changes: 2 additions & 0 deletions include/arch/x86/segment.h
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Expand Up @@ -136,6 +136,8 @@
#define __USER_DS __USER_DS64
#endif

#define __KERN_PERCPU (GDT_PERCPU << 3)

#define _GDT_ENTRY(flags, base, limit) \
((((base) &_U64(0xff000000)) << (56 - 24)) | (((flags) &_U64(0x0000f0ff)) << 40) | \
(((limit) &_U64(0x000f0000)) << (48 - 16)) | (((base) &_U64(0x00ffffff)) << 16) | \
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