L1TFv6 6
Subsystems (10)
v6 cover L1TFv6 6
Latest version of the L1TF OS level mitigation.
v6 only has minor updates addressing last review comments. Few changes to actual generated code.
Andi Kleen (7):
x86, l1tf: Increase 32bit PAE __PHYSICAL_PAGE_MASK x86, l1tf: Protect PROT_NONE PTEs against speculation x86, l1tf: Make sure the first page is always reserved x86, l1tf: Add sysfs reporting for l1tf
x86, l1tf: Report if too much memory for L1TF workaround x86, l1tf: Limit swap file size to MAX_PA/2
mm, l1tf: Disallow non privileged high MMIO PROT_NONE mappings
Linus Torvalds (1):
x86, l1tf: Protect swap entries against L1TF
arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/include/asm/page_32_types.h | 9 ++++-- arch/x86/include/asm/pgtable-2level.h | 17 ++++++++++++ arch/x86/include/asm/pgtable-3level.h | 2 ++ arch/x86/include/asm/pgtable-invert.h | 32 +++++++++++++++++++++ arch/x86/include/asm/pgtable.h | 52 ++++++++++++++++++++++++++--------- arch/x86/include/asm/pgtable_64.h | 38 +++++++++++++++++-------- arch/x86/include/asm/processor.h | 5 ++++ arch/x86/kernel/cpu/bugs.c | 11 ++++++++ arch/x86/kernel/cpu/common.c | 30 ++++++++++++++++++++ arch/x86/kernel/cpu/cpuid-deps.c | 1 + arch/x86/kernel/setup.c | 29 ++++++++++++++++++- arch/x86/mm/init.c | 15 ++++++++++ arch/x86/mm/mmap.c | 21 ++++++++++++++ drivers/base/cpu.c | 8 ++++++ include/asm-generic/pgtable.h | 12 ++++++++ include/linux/cpu.h | 2 ++ include/linux/swapfile.h | 2 ++ mm/memory.c | 37 ++++++++++++++++++------- mm/mprotect.c | 49 +++++++++++++++++++++++++++++++++ mm/swapfile.c | 46 ++++++++++++++++++++----------- 21 files changed, 367 insertions(+), 53 deletions(-) create mode 100644 arch/x86/include/asm/pgtable-invert.h
Signature · 1 line
2.14.3
PATCH v6 1/8 L1TFv6 2
We need to protect memory inside the guest's memory against L1TF.
The hypervisor should already protect itself against the guest by flushing the caches as needed, but pages inside the guest are
not protected against attacks from other processes in that guest.
On 32bit PAE the max PTE mask is currently set to 44 bit because that is the limit imposed by 32bit unsigned long PFNs in the VMs.
The L1TF PROT_NONE protection code uses the PTE masks to determine what bits to invert to make sure the higher bits are set for unmapped entries to prevent L1TF speculation attacks against EPT inside guests.
But our inverted mask has to match the host to provide the full host protection, and the host is likely 64bit and may use more than 43 bits of memory. We want to set all possible bits to be safe here.
So increase the mask on 32bit PAE to 52 to match 64bit.
The real limit is still 44 bits.
All Linux PTEs are created from unsigned long PFNs, so cannot be higher than 44 bits on a 32bit kernel. So these extra PFN bits should be never set. The only users of this macro are using it to look at PTEs, so it's safe.
--- arch/x86/include/asm/page_32_types.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
arch/x86/include/asm/page_32_types.h +7 -2
@@ -29,8 +29,13 @@#define N_EXCEPTION_STACKS 1#ifdef CONFIG_X86_PAE -/* 44=32+12, the limit we can fit into an unsigned long pfn */ -#define __PHYSICAL_MASK_SHIFT 44 +/* +* This is beyond the 44 bit limit imposed by the 32bit long pfns, +* but we need the full mask to make sure inverted PROT_NONE +* entries have all the host bits set in a guest. +* The real limit is still 44 bits. +*/ +#define __PHYSICAL_MASK_SHIFT 52#define __VIRTUAL_MASK_SHIFT 32#else /* !CONFIG_X86_PAE */
Signature · 1 line
2.14.3
PATCH v6 2/8 L1TFv6 8
In reply to Andi KleenWith L1 terminal fault the CPU speculates into unmapped PTEs, and resulting side effects allow to read the memory the PTE is pointing too, if its values are still in the L1 cache.
For swapped out pages Linux uses unmapped PTEs and stores a swap entry into them.
We need to make sure the swap entry is not pointing to valid memory, which requires setting higher bits (between bit 36 and bit 45) that are inside the CPUs physical address space, but outside any real memory.
To do this we invert the offset to make sure the higher bits are always set, as long as the swap file is not too big.
Here's a patch that switches the order of "type" and
"offset" in the x86-64 encoding, in addition to doing the binary 'not' on the offset.
That means that now the offset is bits 9-58 in the page table, and that the type is in the bits that hardware generally doesn't care about.
That, in turn, means that if you have a desktop chip with only 40 bits of physical addressing, now that the offset starts at bit 9, you still have to have 30 bits of offset actually *in use* until bit 39 ends up being clear.
So that's 4 terabyte of swap space (because the offset is counted in pages, so 30 bits of offset is 42 bits of actual coverage). With bigger physical addressing, that obviously grows further, until you hit the limit of the offset (at 50 bits of offset - 62 bits of actual swap file coverage).
Note there is no workaround for 32bit !PAE, or on systems which have more than MAX_PA/2 memory. The later case is very unlikely to happen on real systems.
[updated description and minor tweaks by AK]
--- arch/x86/include/asm/pgtable_64.h | 36 +++++++++++++++++++++++++----------- 1 file changed, 25 insertions(+), 11 deletions(-)
arch/x86/include/asm/pgtable_64.h +25 -11
@@ -273,7 +273,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; }* * | ... | 11| 10| 9|8|7|6|5| 4| 3|2| 1|0| <- bit number * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit names -* | OFFSET (14->63) | TYPE (9-13) |0|0|X|X| X| X|X|SD|0| <- swp entry +* | TYPE (59-63) | ~OFFSET (9-58) |0|0|X|X| X| X|X|SD|0| <- swp entry * * G (8) is aliased and used as a PROT_NONE indicator for * !present ptes. We need to start storing swap entries above
@@ -286,20 +286,34 @@ static inline int pgd_large(pgd_t pgd) { return 0; }* * Bit 7 in swp entry should be 0 because pmd_present checks not only P, * but also L and G. +* +* The offset is inverted by a binary not operation to make the high +* physical bits set. */ -#define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) -#define SWP_TYPE_BITS 5 -/* Place the offset above the type: */ -#define SWP_OFFSET_FIRST_BIT (SWP_TYPE_FIRST_BIT + SWP_TYPE_BITS) +#define SWP_TYPE_BITS 5 + +#define SWP_OFFSET_FIRST_BIT (_PAGE_BIT_PROTNONE + 1) + +/* We always extract/encode the offset by shifting it all the way up, and then down again */ +#define SWP_OFFSET_SHIFT (SWP_OFFSET_FIRST_BIT+SWP_TYPE_BITS)#define MAX_SWAPFILES_CHECK () BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS) -#define __swp_type (x) (((x).val >> (SWP_TYPE_FIRST_BIT)) \ - & ((1U << SWP_TYPE_BITS) - 1)) -#define __swp_offset (x) ((x).val >> SWP_OFFSET_FIRST_BIT) -#define __swp_entry (type, offset) ((swp_entry_t) { \ - ((type) << (SWP_TYPE_FIRST_BIT)) \ - | ((offset) << SWP_OFFSET_FIRST_BIT) }) +/* Extract the high bits for type */ +#define __swp_type (x) ((x).val >> (64 - SWP_TYPE_BITS)) + +/* Shift up (to get rid of type), then down to get value */ +#define __swp_offset (x) (~(x).val << SWP_TYPE_BITS >> SWP_OFFSET_SHIFT) + +/* +* Shift the offset up "too far" by TYPE bits, then down again +* The offset is inverted by a binary not operation to make the high +* physical bits set. +*/ +#define __swp_entry (type, offset) ((swp_entry_t) { \ + (~(unsigned long)(offset) << SWP_OFFSET_SHIFT >> SWP_TYPE_BITS) \ + | ((unsigned long)(type) << (64-SWP_TYPE_BITS)) }) +#define __pte_to_swp_entry (pte) ((swp_entry_t) { pte_val((pte)) })#define __pmd_to_swp_entry (pmd) ((swp_entry_t) { pmd_val((pmd)) })#define __swp_entry_to_pte (x) ((pte_t) { .pte = (x).val })
Signature · 1 line
2.14.3
PATCH v6 3/8 L1TFv6 5
In reply to Andi KleenWe also need to protect PTEs that are set to PROT_NONE against L1TF speculation attacks.
This is important inside guests, because L1TF speculation bypasses physical page remapping. While the VM has its own migitations preventing leaking data from other VMs into the guest, this would still risk leaking the wrong page inside the current guest.
This uses the same technique as Linus' swap entry patch:
while an entry is is in PROTNONE state we invert the complete PFN part part of it. This ensures that the the highest bit will point to non existing memory.
The invert is done by pte/pmd_modify and pfn/pmd/pud_pte for PROTNONE and pte/pmd/pud_pfn undo it.
We assume that noone tries to touch the PFN part of a PTE without using these primitives.
This doesn't handle the case that MMIO is on the top of the CPU physical memory. If such an MMIO region was exposed by an unpriviledged driver for mmap it would be possible to attack some real memory. However this situation is all rather unlikely.
For 32bit non PAE we don't try inversion because there are really not enough bits to protect anything.
Q: Why does the guest need to be protected when the HyperVisor already has L1TF mitigations?
A: Here's an example:
You have physical pages 1 2. They get mapped into a guest as GPA 1 -> PA 2
GPA 2 -> PA 1
through EPT.
The L1TF speculation ignores the EPT remapping.
Now the guest kernel maps GPA 1 to process A and GPA 2 to process B, and they belong to different users and should be isolated.
A sets the GPA 1 PA 2 PTE to PROT_NONE to bypass the EPT remapping and gets read access to the underlying physical page. Which in this case points to PA 2, so it can read process B's data, if it happened to be in L1.
So we broke isolation inside the guest.
There's nothing the hypervisor can do about this. This mitigation has to be done in the guest.
v2: Use new helper to generate XOR mask to invert (Linus)
v3: Use inline helper for protnone mask checking
v4: Use inline helpers to check for PROT_NONE changes
--- arch/x86/include/asm/pgtable-2level.h | 17 ++++++++++++++ arch/x86/include/asm/pgtable-3level.h | 2 ++ arch/x86/include/asm/pgtable-invert.h | 32 +++++++++++++++++++++++++ arch/x86/include/asm/pgtable.h | 44 ++++++++++++++++++++++++----------- arch/x86/include/asm/pgtable_64.h | 2 ++ 5 files changed, 84 insertions(+), 13 deletions(-) create mode 100644 arch/x86/include/asm/pgtable-invert.h
arch/x86/include/asm/pgtable-2level.h +17 -0
@@ -95,4 +95,21 @@ static inline unsigned long pte_bitop(unsigned long value, unsigned int rightshi#define __pte_to_swp_entry (pte) ((swp_entry_t) { (pte).pte_low })#define __swp_entry_to_pte (x) ((pte_t) { .pte = (x).val }) +/* No inverted PFNs on 2 level page tables */ + +static inline u64 protnone_mask (u64 val) +{ +return 0 ; +} + +static inline u64 flip_protnone_guard (u64 oldval,u64 val,u64 mask) +{ +return val; +} + +static inline bool __pte_needs_invert (u64 val) +{ +return false; +} +#endif /* _ASM_X86_PGTABLE_2LEVEL_H */
arch/x86/include/asm/pgtable-3level.h +2 -0
@@ -295,4 +295,6 @@ static inline pte_t gup_get_pte(pte_t *ptep) return pte; } +#include <asm/pgtable-invert.h> +#endif /* _ASM_X86_PGTABLE_3LEVEL_H */
arch/x86/include/asm/pgtable-invert.h new file +32 -0
@@ -0,0 +1,32 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_PGTABLE_INVERT_H +#define _ASM_PGTABLE_INVERT_H 1 + +#ifndef __ASSEMBLY__ + +static inline bool __pte_needs_invert (u64 val) +{ +return (val & (_PAGE_PRESENT|_PAGE_PROTNONE)) == _PAGE_PROTNONE; +} + +/* Get a mask to xor with the page table entry to get the correct pfn. */ +static inline u64 protnone_mask (u64 val) +{ +return __pte_needs_invert (val) ? ~0ull :0 ; +} + +static inline u64 flip_protnone_guard (u64 oldval,u64 val,u64 mask) +{ +/* +* When a PTE transitions from NONE to !NONE or vice-versa +* invert the PFN part to stop speculation. +* pte_pfn undoes this when needed. +*/ +if (__pte_needs_invert (oldval) !=__pte_needs_invert (val)) + val = (val & ~mask) | (~val & mask); +return val; +} + +#endif /* __ASSEMBLY__ */ + +#endif
arch/x86/include/asm/pgtable.h +31 -13
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arch/x86/include/asm/pgtable_64.h +2 -0
@@ -357,5 +357,7 @@ static inline bool gup_fast_permitted(unsigned long start, int nr_pages,return true; } +#include <asm/pgtable-invert.h> +#endif /* !__ASSEMBLY__ */ #endif /* _ASM_X86_PGTABLE_64_H */
Signature · 1 line
2.14.3
PATCH v6 4/8 L1TFv6 4
In reply to Andi KleenThe L1TF workaround doesn't make any attempt to mitigate speculate accesses to the first physical page for zeroed PTEs. Normally it only contains some data from the early real mode BIOS.
I couldn't convince myself we always reserve the first page in all configurations, so add an extra reservation call to make sure it is really reserved. In most configurations (e.g. with the standard reservations) it's likely a nop.
v2: improve comment
--- arch/x86/kernel/setup.c | 6 ++++++ 1 file changed, 6 insertions(+)
arch/x86/kernel/setup.c +6 -0
@@ -823,6 +823,12 @@ void __init setup_arch(char **cmdline_p)memblock_reserve (__pa_symbol (_text), (unsigned long )__bss_stop - (unsigned long )_text); +/* +* Make sure page 0 is always reserved because on systems with +* L1TF its contents can be leaked to user processes. +*/ +memblock_reserve (0 ,PAGE_SIZE ); +early_reserve_initrd ();/*
Signature · 1 line
2.14.3
PATCH v6 5/8 L1TFv6 1
In reply to Andi KleenL1TF core kernel workarounds are cheap and normally always enabled, However we still want to report in sysfs if the system is vulnerable or mitigated. Add the necessary checks.
- We use the same checks as Meltdown to determine if the system is vulnerable. This excludes some Atom CPUs which don't have this problem.
- We check for the (very unlikely) memory > MAX_PA/2 case
- We check for 32bit non PAE and warn
Note this patch will likely conflict with some other workaround patches floating around, but should be straight forward to fix.
v2: Use positive instead of negative flag for WA. Fix override reporting.
v3: Fix L1TF_WA flag settting
v4: Rebase to SSB tree
v5: Minor cleanups. No functional changes.
Don't mark atoms and knights as vulnerable
v6: Change _WA to _FIX
--- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/kernel/cpu/bugs.c | 11 +++++++++++ arch/x86/kernel/cpu/common.c | 30 ++++++++++++++++++++++++++++++ drivers/base/cpu.c | 8 ++++++++ include/linux/cpu.h | 2 ++ 5 files changed, 53 insertions(+)
arch/x86/include/asm/cpufeatures.h +2 -0
@@ -219,6 +219,7 @@#define X86_FEATURE_IBPB ( 7*32+26)/* Indirect Branch Prediction Barrier */ #define X86_FEATURE_STIBP ( 7*32+27)/* Single Thread Indirect Branch Predictors */ #define X86_FEATURE_ZEN ( 7*32+28)/* "" CPU is AMD family 0x17 (Zen) */ +#define X86_FEATURE_L1TF_FIX ( 7*32+29)/* "" L1TF workaround used */ /* Virtualization flags: Linux defined, word 8 */ #define X86_FEATURE_TPR_SHADOW ( 8*32+ 0)/* Intel TPR Shadow */
@@ -371,5 +372,6 @@#define X86_BUG_SPECTRE_V1 X86_BUG(15)/* CPU is affected by Spectre variant 1 attack with conditional branches */ #define X86_BUG_SPECTRE_V2 X86_BUG(16)/* CPU is affected by Spectre variant 2 attack with indirect branches */ #define X86_BUG_SPEC_STORE_BYPASS X86_BUG(17)/* CPU is affected by speculative store bypass attack */ +#define X86_BUG_L1TF X86_BUG(18)/* CPU is affected by L1 Terminal Fault */ #endif /* _ASM_X86_CPUFEATURES_H */
arch/x86/kernel/cpu/bugs.c +11 -0
@@ -707,4 +707,15 @@ ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute * {return cpu_show_common (dev, attr, buf,X86_BUG_SPEC_STORE_BYPASS ); } + +ssize_t cpu_show_l1tf (struct device *dev,struct device_attribute *attr,char *buf) +{ +if (!boot_cpu_has_bug (X86_BUG_L1TF )) +return sprintf (buf,"Not affected\n" ); + +if (boot_cpu_has (X86_FEATURE_L1TF_FIX )) +return sprintf (buf,"Mitigated\n" ); + +return sprintf (buf,"Vulnerable\n" ); +}#endif
arch/x86/kernel/cpu/common.c +30 -0
@@ -924,6 +924,15 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)#endif } +static void __init l1tf_init_workaround (void ) +{ +#if CONFIG_PGTABLE_LEVELS ==2 +pr_warn ("Kernel not compiled for PAE. No workaround for L1TF\n" ); +#else +setup_force_cpu_cap (X86_FEATURE_L1TF_FIX ); +#endif +} +static const __initconst struct x86_cpu_id cpu_no_speculation[] = { {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_CEDARVIEW ,X86_FEATURE_ANY }, {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_CLOVERVIEW ,X86_FEATURE_ANY },
@@ -966,6 +975,21 @@ static const __initconst struct x86_cpu_id cpu_no_spec_store_bypass[] = { {} }; +static const __initconst struct x86_cpu_id cpu_no_l1tf[] = { +/* in addition to cpu_no_speculation */ + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_SILVERMONT1 }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_SILVERMONT2 }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_AIRMONT }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_MERRIFIELD }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_MOOREFIELD }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_GOLDMONT }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_DENVERTON }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_ATOM_GEMINI_LAKE }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_XEON_PHI_KNL }, + {X86_VENDOR_INTEL ,6 ,INTEL_FAM6_XEON_PHI_KNM }, + {} +}; +static void __init cpu_set_bug_bits (struct cpuinfo_x86 *c) {u64 ia32_cap =0 ;
@@ -991,6 +1015,12 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)return ;setup_force_cpu_bug (X86_BUG_CPU_MELTDOWN ); + +if (x86_match_cpu (cpu_no_l1tf)) +return ; + +setup_force_cpu_bug (X86_BUG_L1TF ); +l1tf_init_workaround (); }/*
drivers/base/cpu.c +8 -0
@@ -540,16 +540,24 @@ ssize_t __weak cpu_show_spec_store_bypass(struct device *dev,return sprintf (buf,"Not affected\n" ); } +ssize_t __weak cpu_show_l1tf (struct device *dev, +struct device_attribute *attr,char *buf) +{ +return sprintf (buf,"Not affected\n" ); +} + static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL); static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL); static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL); static DEVICE_ATTR(spec_store_bypass, 0444, cpu_show_spec_store_bypass, NULL); +static DEVICE_ATTR(l1tf, 0444, cpu_show_l1tf, NULL);static struct attribute *cpu_root_vulnerabilities_attrs[] = { &dev_attr_meltdown.attr, &dev_attr_spectre_v1.attr, &dev_attr_spectre_v2.attr, &dev_attr_spec_store_bypass.attr, + &dev_attr_l1tf.attr,NULL };
include/linux/cpu.h +2 -0
@@ -55,6 +55,8 @@ extern ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf);extern ssize_t cpu_show_spec_store_bypass (struct device *dev,struct device_attribute *attr,char *buf); +extern ssize_t cpu_show_l1tf (struct device *dev, +struct device_attribute *attr,char *buf); extern __printf(4, 5) struct device *cpu_device_create(struct device *parent, void *drvdata,
Signature · 1 line
2.14.3
PATCH v6 6/8 L1TFv6 3
In reply to Andi KleenIf the system has more than MAX_PA/2 physical memory the invert page workarounds don't protect the system against the L1TF attack anymore, because an inverted physical address will point to valid memory.
We cannot do much here, after all users want to use the memory, but at least print a warning and report the system as vulnerable in sysfs.
Note this is all extremely unlikely to happen on a real machine because they typically have far more MAX_PA than DIMM slots.
Some VMs also report fairly small PAs to guest, e.g. only 36bits. In this case the threshold will be lower, but applies only to the maximum guest size.
Currently forcing a feature beats clearing it. Since this patch needs to clear a feature that has been forced earlier also fix setup_clear... to prefer clearing over setting.
v2:
Do force clearing in setup_clear_...
Rename variables, fix comments, change formatting.
v3: Use boot_cpu_has_bug. Add l1tf_ Use l1tf_pfn_limit()
v4: Rephrase comment and warning message.
--- arch/x86/kernel/cpu/cpuid-deps.c | 1 + arch/x86/kernel/setup.c | 23 ++++++++++++++++++++++- 2 files changed, 23 insertions(+), 1 deletion(-)
arch/x86/kernel/cpu/cpuid-deps.c +1 -0
@@ -118,4 +118,5 @@ void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)void setup_clear_cpu_cap (unsigned int feature) {do_clear_cpu_cap (NULL , feature); +clear_bit (feature, (unsigned long *)cpu_caps_set); }
arch/x86/kernel/setup.c +22 -1
@@ -785,7 +785,26 @@ static void __init trim_low_memory_range(void) {memblock_reserve (0 ,ALIGN (reserve_low,PAGE_SIZE )); } - + +static __init void l1tf_check_maxpa_memory (void ) +{ +u64 half_pa; + +if (!boot_cpu_has_bug (X86_BUG_L1TF )) +return ; + + half_pa = (u64 )l1tf_pfn_limit () <<PAGE_SHIFT ; + +/* +* This is extremely unlikely to happen because almost all systems have far +* more MAX_PA/2 than can be fit into DIMM slots. +*/ +if (e820__mapped_any (half_pa,ULLONG_MAX - half_pa,E820_TYPE_RAM )) { +pr_warn ("System has more than MAX_PA/2 memory. L1TF workaround not effective.\n" ); +setup_clear_cpu_cap (X86_FEATURE_L1TF_FIX ); + } +} +/* * Dump out kernel offset information on panic. */
@@ -1025,6 +1044,8 @@ void __init setup_arch(char **cmdline_p)insert_resource (&iomem_resource, &data_resource);insert_resource (&iomem_resource, &bss_resource); +l1tf_check_maxpa_memory (); +e820_add_kernel_range ();trim_bios_range ();#ifdef CONFIG_X86_32
Signature · 1 line
2.14.3
PATCH v6 7/8 L1TFv6 7
In reply to Andi KleenFor the L1TF workaround we want to limit the swap file size to below MAX_PA/2, so that the higher bits of the swap offset inverted never point to valid memory.
Add a way for the architecture to override the swap file size check in swapfile.c and add a x86 specific max swapfile check function that enforces that limit.
The check is only enabled if the CPU is vulnerable to L1TF.
In VMs with 42bit MAX_PA the typical limit is 2TB now, on a native system with 46bit PA it is 32TB. The limit is only per individual swap file, so it's always possible to exceed these limits with multiple swap files or partitions.
v2: Use new helper for maxpa_mask computation.
v3: Use l1tf_pfn_limit (Thomas)
Reformat comment
v4: Use boot_cpu_has_bug
--- arch/x86/include/asm/processor.h | 5 +++++ arch/x86/mm/init.c | 15 +++++++++++++ include/linux/swapfile.h | 2 ++ mm/swapfile.c | 46 ++++++++++++++++++++++++++-------------- 4 files changed, 52 insertions(+), 16 deletions(-)
arch/x86/include/asm/processor.h +5 -0
@@ -181,6 +181,11 @@ extern const struct seq_operations cpuinfo_op;extern void cpu_detect (struct cpuinfo_x86 *c); +static inline unsigned long l1tf_pfn_limit (void ) +{ +return BIT (boot_cpu_data.x86_phys_bits -1 -PAGE_SHIFT ) -1 ; +} +extern void early_cpu_init (void );extern void identify_boot_cpu (void );extern void identify_secondary_cpu (struct cpuinfo_x86 *);
arch/x86/mm/init.c +15 -0
@@ -4,6 +4,8 @@#include <linux/swap.h> #include <linux/memblock.h> #include <linux/bootmem.h> /* for max_low_pfn */ +#include <linux/swapfile.h> +#include <linux/swapops.h> #include <asm/set_memory.h> #include <asm/e820/api.h>
@@ -878,3 +880,16 @@ void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache) __cachemode2pte_tbl[cache] =__cm_idx2pte (entry); __pte2cachemode_tbl[entry] = cache; } + +unsigned long max_swapfile_size (void ) +{ +unsigned long pages; + + pages =generic_max_swapfile_size (); + +if (boot_cpu_has_bug (X86_BUG_L1TF )) { +/* Limit the swap file size to MAX_PA/2 for L1TF workaround */ + pages = min_t(unsigned long, l1tf_pfn_limit() + 1, pages); + } +return pages; +}
include/linux/swapfile.h +2 -0
@@ -10,5 +10,7 @@ extern spinlock_t swap_lock;extern struct plist_head swap_active_head;extern struct swap_info_struct *swap_info[];extern int try_to_unuse (unsigned int ,bool ,unsigned long ); +extern unsigned long generic_max_swapfile_size (void ); +extern unsigned long max_swapfile_size (void );#endif /* _LINUX_SWAPFILE_H */
mm/swapfile.c +30 -16
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Signature · 1 line
2.14.3
PATCH v6 8/8 L1TFv6 0
In reply to Andi KleenFor L1TF PROT_NONE mappings are protected by inverting the PFN in the page table entry. This sets the high bits in the CPU's address space, thus making sure to point to not point an unmapped entry to valid cached memory.
Some server system BIOS put the MMIO mappings high up in the physical address space. If such an high mapping was mapped to an unprivileged user they could attack low memory by setting such a mapping to PROT_NONE. This could happen through a special device driver which is not access protected. Normal /dev/mem is of course access protect.
To avoid this we forbid PROT_NONE mappings or mprotect for high MMIO mappings.
Valid page mappings are allowed because the system is then unsafe anyways.
We don't expect users to commonly use PROT_NONE on MMIO. But to minimize any impact here we only do this if the mapping actually refers to a high MMIO address (defined as the MAX_PA-1 bit being set), and also skip the check for root.
For mmaps this is straight forward and can be handled in vm_insert_pfn and in remap_pfn_range().
For mprotect it's a bit trickier. At the point we're looking at the actual PTEs a lot of state has been changed and would be difficult to undo on an error. Since this is a uncommon case we use a separate early page talk walk pass for MMIO PROT_NONE mappings that checks for this condition early. For non MMIO and non PROT_NONE there are no changes.
v2: Use new helpers added earlier
v3: Fix inverted check added in v3
v4: Use l1tf_pfn_limit (Thomas)
Add comment for locked down kernels
squash! mm, l1tf: Disallow non privileged high MMIO PROT_NONE mappings
Use boot_cpu_has_bug
squash! mm, l1tf: Disallow non privileged high MMIO PROT_NONE mappings
Check bug early in arch_has_pfn_modify_check
--- arch/x86/include/asm/pgtable.h | 8 +++++++ arch/x86/mm/mmap.c | 21 ++++++++++++++++++ include/asm-generic/pgtable.h | 12 +++++++++++ mm/memory.c | 37 ++++++++++++++++++++++--------- mm/mprotect.c | 49 ++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 117 insertions(+), 10 deletions(-)
arch/x86/include/asm/pgtable.h +8 -0
@@ -1338,6 +1338,14 @@ static inline bool pud_access_permitted(pud_t pud, bool write) return __pte_access_permitted(pud_val(pud), write); } +#define __HAVE_ARCH_PFN_MODIFY_ALLOWED 1 +extern bool pfn_modify_allowed (unsigned long pfn,pgprot_t prot); + +static inline bool arch_has_pfn_modify_check (void ) +{ +return boot_cpu_has_bug (X86_BUG_L1TF ); +} +#include <asm-generic/pgtable.h> #endif /* __ASSEMBLY__ */
arch/x86/mm/mmap.c +21 -0
@@ -240,3 +240,24 @@ int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)return phys_addr_valid (addr + count -1 ); } + +/* +* Only allow root to set high MMIO mappings to PROT_NONE. +* This prevents an unpriv. user to set them to PROT_NONE and invert +* them, then pointing to valid memory for L1TF speculation. +* +* Note: for locked down kernels may want to disable the root override. +*/ +bool pfn_modify_allowed (unsigned long pfn,pgprot_t prot) +{ +if (!boot_cpu_has_bug (X86_BUG_L1TF )) +return true; +if (!__pte_needs_invert (pgprot_val (prot))) +return true; +/* If it's real memory always allow */ +if (pfn_valid (pfn)) +return true; +if (pfn >l1tf_pfn_limit () && !capable (CAP_SYS_ADMIN )) +return false; +return true; +}
include/asm-generic/pgtable.h +12 -0
@@ -1097,4 +1097,16 @@ static inline void init_espfix_bsp(void) { }#endif #endif +#ifndef __HAVE_ARCH_PFN_MODIFY_ALLOWED +static inline bool pfn_modify_allowed (unsigned long pfn,pgprot_t prot) +{ +return true; +} + +static inline bool arch_has_pfn_modify_check (void ) +{ +return false; +} +#endif +#endif /* _ASM_GENERIC_PGTABLE_H */
mm/memory.c +27 -10
@@ -1891,6 +1891,9 @@ int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,if (addr < vma->vm_start || addr >= vma->vm_end)return -EFAULT ; +if (!pfn_modify_allowed (pfn, pgprot)) +return -EACCES ; +track_pfn_insert (vma, &pgprot,__pfn_to_pfn_t (pfn,PFN_DEV )); ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
@@ -1926,6 +1929,9 @@ static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,track_pfn_insert (vma, &pgprot, pfn); +if (!pfn_modify_allowed (pfn_t_to_pfn (pfn), pgprot)) +return -EACCES ; +/* * If we don't have pte special, then we have to use the pfn_valid() * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
@@ -1973,6 +1979,7 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd, {pte_t *pte;spinlock_t *ptl; +int err =0 ; pte =pte_alloc_map_lock (mm, pmd, addr, &ptl);if (!pte)
@@ -1980,12 +1987,16 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,arch_enter_lazy_mmu_mode ();do {BUG_ON (!pte_none (*pte)); +if (!pfn_modify_allowed (pfn, prot)) { + err = -EACCES ; +break ; + }set_pte_at (mm, addr, pte,pte_mkspecial (pfn_pte (pfn, prot))); pfn++; }while (pte++, addr +=PAGE_SIZE , addr != end);arch_leave_lazy_mmu_mode ();pte_unmap_unlock (pte -1 , ptl); -return 0 ; +return err; } static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
@@ -1994,6 +2005,7 @@ static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud, {pmd_t *pmd;unsigned long next; +int err; pfn -= addr >>PAGE_SHIFT ; pmd =pmd_alloc (mm, pud, addr);
@@ -2002,9 +2014,10 @@ static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,VM_BUG_ON (pmd_trans_huge (*pmd));do { next =pmd_addr_end (addr, end); -if (remap_pte_range (mm, pmd, addr, next, - pfn + (addr >>PAGE_SHIFT ), prot)) -return -ENOMEM ; + err =remap_pte_range (mm, pmd, addr, next, + pfn + (addr >>PAGE_SHIFT ), prot); +if (err) +return err; }while (pmd++, addr = next, addr != end);return 0 ; }
@@ -2015,6 +2028,7 @@ static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d, {pud_t *pud;unsigned long next; +int err; pfn -= addr >>PAGE_SHIFT ; pud =pud_alloc (mm, p4d, addr);
@@ -2022,9 +2036,10 @@ static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d,return -ENOMEM ;do { next =pud_addr_end (addr, end); -if (remap_pmd_range (mm, pud, addr, next, - pfn + (addr >>PAGE_SHIFT ), prot)) -return -ENOMEM ; + err =remap_pmd_range (mm, pud, addr, next, + pfn + (addr >>PAGE_SHIFT ), prot); +if (err) +return err; }while (pud++, addr = next, addr != end);return 0 ; }
@@ -2035,6 +2050,7 @@ static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd, {p4d_t *p4d;unsigned long next; +int err; pfn -= addr >>PAGE_SHIFT ; p4d =p4d_alloc (mm, pgd, addr);
@@ -2042,9 +2058,10 @@ static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,return -ENOMEM ;do { next =p4d_addr_end (addr, end); -if (remap_pud_range (mm, p4d, addr, next, - pfn + (addr >>PAGE_SHIFT ), prot)) -return -ENOMEM ; + err =remap_pud_range (mm, p4d, addr, next, + pfn + (addr >>PAGE_SHIFT ), prot); +if (err) +return err; }while (p4d++, addr = next, addr != end);return 0 ; }
mm/mprotect.c +49 -0
61 lines not on this page · raw message
Signature · 1 line
2.14.3
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[MODERATED] Re: [PATCH v6 5/8] L1TFv6 1
Quoted 15 lines · speck for Andi Kleen
From: Andi Kleen <[email protected]>
Subject: x86, l1tf: Add sysfs reporting for l1tfL1TF core kernel workarounds are cheap and normally always enabled, However we still want to report in sysfs if the system is vulnerable or mitigated. Add the necessary checks.
- We use the same checks as Meltdown to determine if the system is vulnerable. This excludes some Atom CPUs which don't have this problem.
- We check for the (very unlikely) memory > MAX_PA/2 case
- We check for 32bit non PAE and warnNote this patch will likely conflict with some other workaround patches floating around, but should be straight forward to fix.
...
Quoted 9 lines
arch/x86/kernel/cpu/bugs.c +1
-0@@ -707,4 +707,15 @@ ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute * {return cpu_show_common (dev, attr, buf,X86_BUG_SPEC_STORE_BYPASS ); } +
arch/x86/kernel/cpu/bugs.c ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute * · line 720
Quoted 10 lines
arch/x86/kernel/cpu/bugs.c +10
-0+ssize_t cpu_show_l1tf (struct device *dev,struct device_attribute *attr,char *buf) +{ +if (!boot_cpu_has_bug (X86_BUG_L1TF )) +return sprintf (buf,"Not affected\n" ); + +if (boot_cpu_has (X86_FEATURE_L1TF_FIX )) +return sprintf (buf,"Mitigated\n" ); + +return sprintf (buf,"Vulnerable\n" ); +}
In case you've missed it from the last round:
Make that function call cpu_show_common() like the others do.
Signature · 5 lines
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 8 lines · speck for Andi Kleen
From: Andi Kleen <[email protected]>
Subject: x86, l1tf: Report if too much memory for L1TF
workaroundIf the system has more than MAX_PA/2 physical memory the invert page workarounds don't protect the system against the L1TF attack anymore, because an inverted physical address will point to valid memory.
I realise I am late to this particular party (so apologies if it has been discussed before), but there is something which can be done here.
One option is to simply ignore any RAM above the PA/2 boundary. If you never actually use it, there will be no data to leak even if the inverted pfn ends up pointing to cacheable memory. This in particular will help with systems which unhealthy habit of starting their ACPI DIMM Hotplug regions at a stupidly high address.
This doesn't work so well for any PMEM above the boundary, which has a rather higher chance of having something interesting to peek at.
Going out further on a limb, it might be possible to play with the MTRRs to make PA/2 to MAX become UC, in the case that we've decided to try and ignore it as a mitigation.
~Andrew
[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 10 lines · speck for Andrew Cooper
Quoted 8 lines · speck for Andi Kleen
From: Andi Kleen <[email protected]>
Subject: x86, l1tf: Report if too much memory for L1TF
workaroundIf the system has more than MAX_PA/2 physical memory the invert page workarounds don't protect the system against the L1TF attack anymore, because an inverted physical address will point to valid memory.
Quoted 4 lines
I realise I am late to this particular party (so apologies if it has been discussed before), but there is something which can be done here.
One option is to simply ignore any RAM above the PA/2 boundary. If you
I had this in a earlier patch kit, but Linus didn't like it and pointed out that the people who have that much memory will likely prefer to use it. So now we just warn.
-Andi
[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 4 lines · speck for Andi Kleen
I had this in a earlier patch kit, but Linus didn't like it and pointed out that the people who have that much memory will likely prefer to use it. So now we just warn.
I actually wonder if such people really even exist to begin with. The warning might get some of them to come out of the woodwork, and then we might see what they actually do.
If they are HPC people, they will definitely just want their RAM, I suspect.
Linus
[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 10 lines · speck for Linus Torvalds
Quoted 3 lines · speck for Andi Kleen
I had this in a earlier patch kit, but Linus didn't like it and pointed out that the people who have that much memory will likely prefer to use it. So now we just warn.
I actually wonder if such people really even exist to begin with. The warning might get some of them to come out of the woodwork, and then we might see what they actually do.
If they are HPC people, they will definitely just want their RAM, I suspect.
Yeah - thinking about it, I'm not so sure either.
The price markup on servers that large puts them firmly outside the $ per U calculation that most clouds would be looking for. The biggest server I've encountered is (IIRC - I'll need to double check the logs) a 64TB Skylake system from Lenovo, so clearly there is at least some kind of market for systems that size.
HPC are going to be single workload setups. I expect there will be other bespoke systems which are that large, but I expect they wont be running mutually-distrustful workloads.
~Andrew
(/me crosses one item of the TODO list for Xen)
[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 4 lines · speck for Andrew Cooper
HPC are going to be single workload setups. I expect there will be other bespoke systems which are that large, but I expect they wont be running mutually-distrustful workloads.
From what I've seen, the big-memory people are all either HPC or doing big databases, and want all the memory they can get.
And yeah, they aren't running other peoples jobs.
But we'll see. The desktop chips have smaller PA limits. But then you tend to be limited by just memory channels anyway - ie a desktop chip might be limited to "just" 39 bits of physical memory, but in practice the RAM limit is much much lower simply due to memory controllers.
So let's see if the warning ever triggers, and ask people then.
Linus
[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 4 lines
But we'll see. The desktop chips have smaller PA limits. But then you tend to be limited by just memory channels anyway - ie a desktop chip might be limited to "just" 39 bits of physical memory, but in practice the RAM limit is much much lower simply due to memory controllers.
The only systems that should be able to hit it are systems with a lot of sockets (>8S)
-Andi
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Dave Hansen
maintainer[MODERATED] Re: [PATCH v6 1/8] L1TFv6 2
Quoted 5 lines · speck for Andi Kleen
But our inverted mask has to match the host to provide the full host protection, and the host is likely 64bit and may use more than 43 bits of memory. We want to set all possible bits to be safe here.
So increase the mask on 32bit PAE to 52 to match 64bit.
I'm going to harp on the patch description a bit more. I know some of this stuff is obvious to you at this point, but it was clear as mud to me the first time I read it (I totally got it wrong) and I'm not _entirely_ uninformed about this stuff.
*Please* add a simple sentence about what the attack vector is, making it clear that the attacker here is a guest application, and that it can attack other apps or the guest kernel:
Mitigates: A guest application using PROT_NONE/L1TF to attack other guest applications or guest kernel memory.
I'd also really appreciate a simple, practical example of what this means:
For example: Without this patch, a guest PTE that pointed to guest phyiscal address 1GB that was made a (mitigated) PROT_NONE PTE would "point" to just below 16TB (2^44 == 16TB). If the host has that much memory, and the corresponding host physical memory from ~16TB was mapped to the *same* guest, a guest application might be able to access the contents via an L1TF attack.
I think there are also two lesser things that the changelog is missing, but
The larger the guest's physical address space, the larger of a *host* window starting at 16TB it can attack, if memory in that window is mapped into the guest.
On hosts that have all their guest memory under 8TB, this provides no mitigation. That's not going top be super common, but the mitigation here is basically zero cost.
[MODERATED] Re: [PATCH v6 1/8] L1TFv6 2
Quoted 1 line · speck for Dave Hansen
I'm going to harp on the patch description a bit more. I know some of
Have you actually read the description of
x86, l1tf: Protect PROT_NONE PTEs against speculation
?
Quoted 7 lines
this stuff is obvious to you at this point, but it was clear as mud to me the first time I read it (I totally got it wrong) and I'm not _entirely_ uninformed about this stuff.
*Please* add a simple sentence about what the attack vector is, making it clear that the attacker here is a guest application, and that it can attack other apps or the guest kernel:
This is all explained in the other patch that implements the PROT_NONE protection.
You want to duplicate that description into every other patch?
Not repeating the descriptions in other patches is common practice in Linux changelogs. Violating that principle would lead to tons of redundant descriptions, annoying everyone who actually reviews the whole patchkit.
Quoted 5 lines
Mitigates: A guest application using PROT_NONE/L1TF to attack other guest applications or guest kernel memory.
I'd also really appreciate a simple, practical example of what this means:
Already in the other description in a detailed example.
-Andi
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[MODERATED] Re: [PATCH v6 6/8] L1TFv6 3
Quoted 54 lines · speck for Andi Kleen
From: Andi Kleen <[email protected]>
Subject: x86, l1tf: Report if too much memory for L1TF
workaroundIf the system has more than MAX_PA/2 physical memory the invert page workarounds don't protect the system against the L1TF attack anymore, because an inverted physical address will point to valid memory.
We cannot do much here, after all users want to use the memory, but at least print a warning and report the system as vulnerable in sysfs.
Note this is all extremely unlikely to happen on a real machine because they typically have far more
MAX_PAthan DIMM slots.Some VMs also report fairly small PAs to guest, e.g. only 36bits. In this case the threshold will be lower, but applies only to the maximum guest size.
Currently forcing a feature beats clearing it. Since this patch needs to clear a feature that has been forced earlier also fix
setup_clear... to prefer clearing over setting.v2:
Do force clearing insetup_clear_...
Rename variables, fix comments, change formatting.
v3: Useboot_cpu_has_bug. Addl1tf_Usel1tf_pfn_limit()
v4: Rephrase comment and warning message.Signed-off-by Andi Kleen <[email protected]>--- arch/x86/kernel/cpu/cpuid-deps.c | 1 + arch/x86/kernel/setup.c | 23 ++++++++++++++++++++++- 2 files changed, 23 insertions(+), 1 deletion(-)arch/x86/kernel/cpu/cpuid-deps.c +1
-0@@ -118,4 +118,5 @@ void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)void setup_clear_cpu_cap (unsigned int feature) {do_clear_cpu_cap (NULL , feature); +clear_bit (feature, (unsigned long *)cpu_caps_set); }arch/x86/kernel/setup.c +0
-0@@ -785,7 +785,26 @@ static void __init trim_low_memory_range(void) {memblock_reserve (0 ,ALIGN (reserve_low,PAGE_SIZE )); }
arch/x86/kernel/setup.c static void __init trim_low_memory_range(void) · line 796
Quoted 10 lines
arch/x86/kernel/setup.c +9
-1- + +static __init void l1tf_check_maxpa_memory (void ) +{ +u64 half_pa; + +if (!boot_cpu_has_bug (X86_BUG_L1TF )) +return ; + + half_pa = (u64 )l1tf_pfn_limit () <<PAGE_SHIFT ;
This breaks bisection -- l1tf_pfn_limit() is introduced in the next patch. The patches can probably just be swapped.
Signature · 1 line
Josh
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[MODERATED] Re: [PATCH v6 5/8] L1TFv6 1
Review
Quoted 10 lines · speck for Andi Kleen
(quoted diff) +10
-0+ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf) +{ + if (!boot_cpu_has_bug(X86_BUG_L1TF)) + return sprintf(buf, "Not affected\n"); + + if (boot_cpu_has(X86_FEATURE_L1TF_FIX)) + return sprintf(buf, "Mitigated\n"); + + return sprintf(buf, "Vulnerable\n"); +}
Once all the virt pieces are in place (HT disabled, vmexit flush) how are we going to report the status in sysfs?
For example, if somebody started a (potentially untrusted) VM without disabling HT, how do we report that?
Signature · 1 line
Josh