From 322f8b8b340c824aef891342b0f5795d15e11562 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 30 Dec 2017 22:13:53 +0100 Subject: [PATCH 1/4] x86/smpboot: Remove stale TLB flush invocations smpboot_setup_warm_reset_vector() and smpboot_restore_warm_reset_vector() invoke local_flush_tlb() for no obvious reason. Digging in history revealed that the original code in the 2.1 era added those because the code manipulated a swapper_pg_dir pagetable entry. The pagetable manipulation was removed long ago in the 2.3 timeframe, but the TLB flush invocations stayed around forever. Remove them along with the pointless pr_debug()s which come from the same 2.1 change. Reported-by: Dominik Brodowski Signed-off-by: Thomas Gleixner Cc: Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Linus Torvalds Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20171230211829.586548655@linutronix.de Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 33d6000265aa75..c3402fc30865ca 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -128,25 +128,16 @@ static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip) spin_lock_irqsave(&rtc_lock, flags); CMOS_WRITE(0xa, 0xf); spin_unlock_irqrestore(&rtc_lock, flags); - local_flush_tlb(); - pr_debug("1.\n"); *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) = start_eip >> 4; - pr_debug("2.\n"); *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = start_eip & 0xf; - pr_debug("3.\n"); } static inline void smpboot_restore_warm_reset_vector(void) { unsigned long flags; - /* - * Install writable page 0 entry to set BIOS data area. - */ - local_flush_tlb(); - /* * Paranoid: Set warm reset code and vector here back * to default values. From decab0888e6e14e11d53cefa85f8b3d3b45ce73c Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 30 Dec 2017 22:13:54 +0100 Subject: [PATCH 2/4] x86/mm: Remove preempt_disable/enable() from __native_flush_tlb() The preempt_disable/enable() pair in __native_flush_tlb() was added in commit: 5cf0791da5c1 ("x86/mm: Disable preemption during CR3 read+write") ... to protect the UP variant of flush_tlb_mm_range(). That preempt_disable/enable() pair should have been added to the UP variant of flush_tlb_mm_range() instead. The UP variant was removed with commit: ce4a4e565f52 ("x86/mm: Remove the UP asm/tlbflush.h code, always use the (formerly) SMP code") ... but the preempt_disable/enable() pair stayed around. The latest change to __native_flush_tlb() in commit: 6fd166aae78c ("x86/mm: Use/Fix PCID to optimize user/kernel switches") ... added an access to a per CPU variable outside the preempt disabled regions, which makes no sense at all. __native_flush_tlb() must always be called with at least preemption disabled. Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch bad callers independent of the smp_processor_id() debugging. Signed-off-by: Thomas Gleixner Cc: Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Dominik Brodowski Cc: Linus Torvalds Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20171230211829.679325424@linutronix.de Signed-off-by: Ingo Molnar --- arch/x86/include/asm/tlbflush.h | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index b519da4fc03c7c..f9b48ce152ebac 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -345,15 +345,17 @@ static inline void invalidate_user_asid(u16 asid) */ static inline void __native_flush_tlb(void) { - invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); /* - * If current->mm == NULL then we borrow a mm which may change - * during a task switch and therefore we must not be preempted - * while we write CR3 back: + * Preemption or interrupts must be disabled to protect the access + * to the per CPU variable and to prevent being preempted between + * read_cr3() and write_cr3(). */ - preempt_disable(); + WARN_ON_ONCE(preemptible()); + + invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid)); + + /* If current->mm == NULL then the read_cr3() "borrows" an mm */ native_write_cr3(__native_read_cr3()); - preempt_enable(); } /* From a62d69857aab4caa43049e72fe0ed5c4a60518dd Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 31 Dec 2017 11:24:34 +0100 Subject: [PATCH 3/4] x86/ldt: Plug memory leak in error path The error path in write_ldt() tries to free 'old_ldt' instead of the newly allocated 'new_ldt', resulting in a memory leak. It also misses to clean up a half populated LDT pagetable, which is not a leak as it gets cleaned up when the process exits. Free both the potentially half populated LDT pagetable and the newly allocated LDT struct. This can be done unconditionally because once an LDT is mapped subsequent maps will succeed, because the PTE page is already populated and the two LDTs fit into that single page. Reported-by: Mathieu Desnoyers Signed-off-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Dominik Brodowski Cc: Linus Torvalds Cc: Linus Torvalds Cc: Peter Zijlstra Fixes: f55f0501cbf6 ("x86/pti: Put the LDT in its own PGD if PTI is on") Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1712311121340.1899@nanos Signed-off-by: Ingo Molnar --- arch/x86/kernel/ldt.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 579cc4a66fdf66..500e90e44f8669 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -421,7 +421,13 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) */ error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0); if (error) { - free_ldt_struct(old_ldt); + /* + * This only can fail for the first LDT setup. If an LDT is + * already installed then the PTE page is already + * populated. Mop up a half populated page table. + */ + free_ldt_pgtables(mm); + free_ldt_struct(new_ldt); goto out_unlock; } From 7f414195b0c3612acd12b4611a5fe75995cf10c7 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 31 Dec 2017 16:52:15 +0100 Subject: [PATCH 4/4] x86/ldt: Make LDT pgtable free conditional Andy prefers to be paranoid about the pagetable free in the error path of write_ldt(). Make it conditional and warn whenever the installment of a secondary LDT fails. Requested-by: Andy Lutomirski Signed-off-by: Thomas Gleixner --- arch/x86/kernel/ldt.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 500e90e44f8669..26d713ecad34a8 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -426,7 +426,8 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) * already installed then the PTE page is already * populated. Mop up a half populated page table. */ - free_ldt_pgtables(mm); + if (!WARN_ON_ONCE(old_ldt)) + free_ldt_pgtables(mm); free_ldt_struct(new_ldt); goto out_unlock; }