The following commit has been merged into the x86/iopl branch of tip: Commit-ID: ede65f28e61e5a5ccf6c46d9c8169abbd89fe24d Gitweb: https://git.kernel.org/tip/ede65f28e61e5a5ccf6c46d9c8169abbd89fe24d Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Wed, 13 Nov 2019 21:42:57 +01:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Thu, 14 Nov 2019 20:15:07 +01:00 x86/iopl: Restrict iopl() permission scope The access to the full I/O port range can be also provided by the TSS I/O bitmap, but that would require to copy 8k of data on scheduling in the task. As shown with the sched out optimization TSS.io_bitmap_base can be used to switch the incoming task to a preallocated I/O bitmap which has all bits zero, i.e. allows access to all I/O ports. Implementing this allows to provide an iopl() emulation mode which restricts the IOPL level 3 permissions to I/O port access but removes the STI/CLI permission which is coming with the hardware IOPL mechansim. Provide a config option to switch IOPL to emulation mode, make it the default and while at it also provide an option to disable IOPL completely. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20191113210105.369055550@xxxxxxxxxxxxx --- arch/x86/Kconfig | 32 +++++++++- arch/x86/include/asm/pgtable_32_types.h | 2 +- arch/x86/include/asm/processor.h | 28 ++++++-- arch/x86/kernel/cpu/common.c | 5 +- arch/x86/kernel/ioport.c | 87 ++++++++++++++++-------- arch/x86/kernel/process.c | 32 +++++---- 6 files changed, 139 insertions(+), 47 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index d6e1faa..2aad1cd 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1254,6 +1254,38 @@ config X86_VSYSCALL_EMULATION Disabling this option saves about 7K of kernel size and possibly 4K of additional runtime pagetable memory. +choice + prompt "IOPL" + default X86_IOPL_EMULATION + +config X86_IOPL_EMULATION + bool "IOPL Emulation" + ---help--- + Legacy IOPL support is an overbroad mechanism which allows user + space aside of accessing all 65536 I/O ports also to disable + interrupts. To gain this access the caller needs CAP_SYS_RAWIO + capabilities and permission from potentially active security + modules. + + The emulation restricts the functionality of the syscall to + only allowing the full range I/O port access, but prevents the + ability to disable interrupts from user space. + +config X86_IOPL_LEGACY + bool "IOPL Legacy" + ---help--- + Allow the full IOPL permissions, i.e. user space access to all + 65536 I/O ports and also the ability to disable interrupts, which + is overbroad and can result in system lockups. + +config X86_IOPL_NONE + bool "IOPL None" + ---help--- + Disable the IOPL permission syscall. That's the safest option as + no sane application should depend on this functionality. + +endchoice + config TOSHIBA tristate "Toshiba Laptop support" depends on X86_32 diff --git a/arch/x86/include/asm/pgtable_32_types.h b/arch/x86/include/asm/pgtable_32_types.h index b0bc0ff..0fab4bf 100644 --- a/arch/x86/include/asm/pgtable_32_types.h +++ b/arch/x86/include/asm/pgtable_32_types.h @@ -44,7 +44,7 @@ extern bool __vmalloc_start_set; /* set once high_memory is set */ * Define this here and validate with BUILD_BUG_ON() in pgtable_32.c * to avoid include recursion hell */ -#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 40) +#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 41) #define CPU_ENTRY_AREA_BASE \ ((FIXADDR_TOT_START - PAGE_SIZE * (CPU_ENTRY_AREA_PAGES + 1)) \ diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 40bb0f7..b0e02aa 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -332,19 +332,21 @@ struct x86_hw_tss { #define IO_BITMAP_BYTES (IO_BITMAP_BITS / BITS_PER_BYTE) #define IO_BITMAP_LONGS (IO_BITMAP_BYTES / sizeof(long)) -#define IO_BITMAP_OFFSET_VALID \ +#define IO_BITMAP_OFFSET_VALID_MAP \ (offsetof(struct tss_struct, io_bitmap.bitmap) - \ offsetof(struct tss_struct, x86_tss)) +#define IO_BITMAP_OFFSET_VALID_ALL \ + (offsetof(struct tss_struct, io_bitmap.mapall) - \ + offsetof(struct tss_struct, x86_tss)) + /* - * sizeof(unsigned long) coming from an extra "long" at the end - * of the iobitmap. - * - * -1? seg base+limit should be pointing to the address of the - * last valid byte + * sizeof(unsigned long) coming from an extra "long" at the end of the + * iobitmap. The limit is inclusive, i.e. the last valid byte. */ #define __KERNEL_TSS_LIMIT \ - (IO_BITMAP_OFFSET_VALID + IO_BITMAP_BYTES + sizeof(unsigned long) - 1) + (IO_BITMAP_OFFSET_VALID_ALL + IO_BITMAP_BYTES + \ + sizeof(unsigned long) - 1) /* Base offset outside of TSS_LIMIT so unpriviledged IO causes #GP */ #define IO_BITMAP_OFFSET_INVALID (__KERNEL_TSS_LIMIT + 1) @@ -380,6 +382,12 @@ struct x86_io_bitmap { * be within the limit. */ unsigned long bitmap[IO_BITMAP_LONGS + 1]; + + /* + * Special I/O bitmap to emulate IOPL(3). All bytes zero, + * except the additional byte at the end. + */ + unsigned long mapall[IO_BITMAP_LONGS + 1]; }; struct tss_struct { @@ -506,7 +514,13 @@ struct thread_struct { #endif /* IO permissions: */ struct io_bitmap *io_bitmap; + + /* + * IOPL. Priviledge level dependent I/O permission which includes + * user space CLI/STI when granted. + */ unsigned long iopl; + unsigned long iopl_emul; mm_segment_t addr_limit; diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 79dd544..7bf402b 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1864,6 +1864,11 @@ void cpu_init(void) tss->io_bitmap.prev_max = 0; tss->io_bitmap.prev_sequence = 0; memset(tss->io_bitmap.bitmap, 0xff, sizeof(tss->io_bitmap.bitmap)); + /* + * Invalidate the extra array entry past the end of the all + * permission bitmap as required by the hardware. + */ + tss->io_bitmap.mapall[IO_BITMAP_LONGS] = ~0UL; set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss); load_TR_desc(); diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c index 3548563..9ed9458 100644 --- a/arch/x86/kernel/ioport.c +++ b/arch/x86/kernel/ioport.c @@ -17,25 +17,41 @@ static atomic64_t io_bitmap_sequence; void io_bitmap_share(struct task_struct *tsk) - { - /* - * Take a refcount on current's bitmap. It can be used by - * both tasks as long as none of them changes the bitmap. - */ - refcount_inc(¤t->thread.io_bitmap->refcnt); - tsk->thread.io_bitmap = current->thread.io_bitmap; +{ + /* Can be NULL when current->thread.iopl_emul == 3 */ + if (current->thread.io_bitmap) { + /* + * Take a refcount on current's bitmap. It can be used by + * both tasks as long as none of them changes the bitmap. + */ + refcount_inc(¤t->thread.io_bitmap->refcnt); + tsk->thread.io_bitmap = current->thread.io_bitmap; + } set_tsk_thread_flag(tsk, TIF_IO_BITMAP); } +static void task_update_io_bitmap(void) +{ + struct thread_struct *t = ¤t->thread; + + if (t->iopl_emul == 3 || t->io_bitmap) { + /* TSS update is handled on exit to user space */ + set_thread_flag(TIF_IO_BITMAP); + } else { + clear_thread_flag(TIF_IO_BITMAP); + /* Invalidate TSS */ + preempt_disable(); + tss_update_io_bitmap(); + preempt_enable(); + } +} + void io_bitmap_exit(void) { struct io_bitmap *iobm = current->thread.io_bitmap; current->thread.io_bitmap = NULL; - clear_thread_flag(TIF_IO_BITMAP); - preempt_disable(); - tss_update_io_bitmap(); - preempt_enable(); + task_update_io_bitmap(); if (iobm && refcount_dec_and_test(&iobm->refcnt)) kfree(iobm); } @@ -157,36 +173,55 @@ SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on) */ SYSCALL_DEFINE1(iopl, unsigned int, level) { - struct pt_regs *regs = current_pt_regs(); struct thread_struct *t = ¤t->thread; + struct pt_regs *regs = current_pt_regs(); + unsigned int old; /* * Careful: the IOPL bits in regs->flags are undefined under Xen PV * and changing them has no effect. */ - unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT; + if (IS_ENABLED(CONFIG_X86_IOPL_NONE)) + return -ENOSYS; if (level > 3) return -EINVAL; + + if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) + old = t->iopl_emul; + else + old = t->iopl >> X86_EFLAGS_IOPL_BIT; + + /* No point in going further if nothing changes */ + if (level == old) + return 0; + /* Trying to gain more privileges? */ if (level > old) { if (!capable(CAP_SYS_RAWIO) || security_locked_down(LOCKDOWN_IOPORT)) return -EPERM; } - /* - * Change the flags value on the return stack, which has been set - * up on system-call entry. See also the fork and signal handling - * code how this is handled. - */ - regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | - (level << X86_EFLAGS_IOPL_BIT); - /* Store the new level in the thread struct */ - t->iopl = level << X86_EFLAGS_IOPL_BIT; - /* - * X86_32 switches immediately and XEN handles it via emulation. - */ - set_iopl_mask(t->iopl); + + if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) { + t->iopl_emul = level; + task_update_io_bitmap(); + } else { + /* + * Change the flags value on the return stack, which has + * been set up on system-call entry. See also the fork and + * signal handling code how this is handled. + */ + regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | + (level << X86_EFLAGS_IOPL_BIT); + /* Store the new level in the thread struct */ + t->iopl = level << X86_EFLAGS_IOPL_BIT; + /* + * X86_32 switches immediately and XEN handles it via + * emulation. + */ + set_iopl_mask(t->iopl); + } return 0; } diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index bfc935d..8ba2707 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -370,21 +370,27 @@ static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm) void tss_update_io_bitmap(void) { struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw); + u16 *base = &tss->x86_tss.io_bitmap_base; if (test_thread_flag(TIF_IO_BITMAP)) { - struct io_bitmap *iobm = current->thread.io_bitmap; - - /* - * Only copy bitmap data when the sequence number - * differs. The update time is accounted to the incoming - * task. - */ - if (tss->io_bitmap.prev_sequence != iobm->sequence) - tss_copy_io_bitmap(tss, iobm); - - /* Enable the bitmap */ - tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID; - + struct thread_struct *t = ¤t->thread; + + if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION) && + t->iopl_emul == 3) { + *base = IO_BITMAP_OFFSET_VALID_ALL; + } else { + struct io_bitmap *iobm = t->io_bitmap; + /* + * Only copy bitmap data when the sequence number + * differs. The update time is accounted to the + * incoming task. + */ + if (tss->io_bitmap.prev_sequence != iobm->sequence) + tss_copy_io_bitmap(tss, iobm); + + /* Enable the bitmap */ + *base = IO_BITMAP_OFFSET_VALID_MAP; + } /* * Make sure that the TSS limit is covering the io bitmap. * It might have been cut down by a VMEXIT to 0x67 which
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