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Subject[GIT pull] x86/pti - The final bits and fixes
Linus,

please pull the latest x86-pti-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-pti-for-linus

This last update contains:

- An objtool fix to prevent a segfault with the gold linker by
changing the invocation order. That's not just for gold, it's a
general robustness improvement.

- An improved error message for objtool which spares tearing hairs.

- Make KASAN fail loudly if there is not enough memory instead of
oopsing at some random place later

- RSB fill on context switch to prevent RSB underflow and speculation
through other units.

- Make the retpoline/RSB functionality work reliably for both Intel and
AMD

- Add retpoline to the module version magic so mismatch can be detected

- A small (non-fix) update for cpufeatures which prevents cpu feature
clashing for the upcoming extra mitigation bits to easy backporting.

The objtool invocation order change results in a trivial merge
conflict. Just make sure objtool is invoked before modversions.

Thanks,

tglx

------------------>
Andi Kleen (1):
module: Add retpoline tag to VERMAGIC

Andrey Ryabinin (1):
x86/kasan: Panic if there is not enough memory to boot

David Woodhouse (1):
x86/retpoline: Fill RSB on context switch for affected CPUs

Josh Poimboeuf (2):
objtool: Fix seg fault with gold linker
objtool: Improve error message for bad file argument

Paolo Bonzini (1):
x86/cpufeature: Move processor tracing out of scattered features

Tom Lendacky (1):
x86/retpoline: Add LFENCE to the retpoline/RSB filling RSB macros


arch/x86/entry/entry_32.S | 11 +++++++++++
arch/x86/entry/entry_64.S | 11 +++++++++++
arch/x86/include/asm/cpufeatures.h | 3 ++-
arch/x86/include/asm/nospec-branch.h | 6 +++++-
arch/x86/kernel/cpu/bugs.c | 36 ++++++++++++++++++++++++++++++++++++
arch/x86/kernel/cpu/scattered.c | 1 -
arch/x86/mm/kasan_init_64.c | 24 ++++++++++++++----------
include/linux/vermagic.h | 8 +++++++-
scripts/Makefile.build | 14 ++++++++++----
tools/objtool/elf.c | 4 +++-
10 files changed, 99 insertions(+), 19 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a1f28a54f23a..60c4c342316c 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -244,6 +244,17 @@ ENTRY(__switch_to_asm)
movl %ebx, PER_CPU_VAR(stack_canary)+stack_canary_offset
#endif

+#ifdef CONFIG_RETPOLINE
+ /*
+ * When switching from a shallower to a deeper call stack
+ * the RSB may either underflow or use entries populated
+ * with userspace addresses. On CPUs where those concerns
+ * exist, overwrite the RSB with entries which capture
+ * speculative execution to prevent attack.
+ */
+ FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
+#endif
+
/* restore callee-saved registers */
popl %esi
popl %edi
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 59874bc1aed2..d54a0ede61d1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -487,6 +487,17 @@ ENTRY(__switch_to_asm)
movq %rbx, PER_CPU_VAR(irq_stack_union)+stack_canary_offset
#endif

+#ifdef CONFIG_RETPOLINE
+ /*
+ * When switching from a shallower to a deeper call stack
+ * the RSB may either underflow or use entries populated
+ * with userspace addresses. On CPUs where those concerns
+ * exist, overwrite the RSB with entries which capture
+ * speculative execution to prevent attack.
+ */
+ FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
+#endif
+
/* restore callee-saved registers */
popq %r15
popq %r14
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index f275447862f4..25b9375c1484 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -206,11 +206,11 @@
#define X86_FEATURE_RETPOLINE ( 7*32+12) /* Generic Retpoline mitigation for Spectre variant 2 */
#define X86_FEATURE_RETPOLINE_AMD ( 7*32+13) /* AMD Retpoline mitigation for Spectre variant 2 */
#define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory Number */
-#define X86_FEATURE_INTEL_PT ( 7*32+15) /* Intel Processor Trace */
#define X86_FEATURE_AVX512_4VNNIW ( 7*32+16) /* AVX-512 Neural Network Instructions */
#define X86_FEATURE_AVX512_4FMAPS ( 7*32+17) /* AVX-512 Multiply Accumulation Single precision */

#define X86_FEATURE_MBA ( 7*32+18) /* Memory Bandwidth Allocation */
+#define X86_FEATURE_RSB_CTXSW ( 7*32+19) /* Fill RSB on context switches */

/* Virtualization flags: Linux defined, word 8 */
#define X86_FEATURE_TPR_SHADOW ( 8*32+ 0) /* Intel TPR Shadow */
@@ -245,6 +245,7 @@
#define X86_FEATURE_AVX512IFMA ( 9*32+21) /* AVX-512 Integer Fused Multiply-Add instructions */
#define X86_FEATURE_CLFLUSHOPT ( 9*32+23) /* CLFLUSHOPT instruction */
#define X86_FEATURE_CLWB ( 9*32+24) /* CLWB instruction */
+#define X86_FEATURE_INTEL_PT ( 9*32+25) /* Intel Processor Trace */
#define X86_FEATURE_AVX512PF ( 9*32+26) /* AVX-512 Prefetch */
#define X86_FEATURE_AVX512ER ( 9*32+27) /* AVX-512 Exponential and Reciprocal */
#define X86_FEATURE_AVX512CD ( 9*32+28) /* AVX-512 Conflict Detection */
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 402a11c803c3..7b45d8424150 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -11,7 +11,7 @@
* Fill the CPU return stack buffer.
*
* Each entry in the RSB, if used for a speculative 'ret', contains an
- * infinite 'pause; jmp' loop to capture speculative execution.
+ * infinite 'pause; lfence; jmp' loop to capture speculative execution.
*
* This is required in various cases for retpoline and IBRS-based
* mitigations for the Spectre variant 2 vulnerability. Sometimes to
@@ -38,11 +38,13 @@
call 772f; \
773: /* speculation trap */ \
pause; \
+ lfence; \
jmp 773b; \
772: \
call 774f; \
775: /* speculation trap */ \
pause; \
+ lfence; \
jmp 775b; \
774: \
dec reg; \
@@ -73,6 +75,7 @@
call .Ldo_rop_\@
.Lspec_trap_\@:
pause
+ lfence
jmp .Lspec_trap_\@
.Ldo_rop_\@:
mov \reg, (%_ASM_SP)
@@ -165,6 +168,7 @@
" .align 16\n" \
"901: call 903f;\n" \
"902: pause;\n" \
+ " lfence;\n" \
" jmp 902b;\n" \
" .align 16\n" \
"903: addl $4, %%esp;\n" \
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e4dc26185aa7..390b3dc3d438 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -23,6 +23,7 @@
#include <asm/alternative.h>
#include <asm/pgtable.h>
#include <asm/set_memory.h>
+#include <asm/intel-family.h>

static void __init spectre_v2_select_mitigation(void);

@@ -155,6 +156,23 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
return SPECTRE_V2_CMD_NONE;
}

+/* Check for Skylake-like CPUs (for RSB handling) */
+static bool __init is_skylake_era(void)
+{
+ if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+ boot_cpu_data.x86 == 6) {
+ switch (boot_cpu_data.x86_model) {
+ case INTEL_FAM6_SKYLAKE_MOBILE:
+ case INTEL_FAM6_SKYLAKE_DESKTOP:
+ case INTEL_FAM6_SKYLAKE_X:
+ case INTEL_FAM6_KABYLAKE_MOBILE:
+ case INTEL_FAM6_KABYLAKE_DESKTOP:
+ return true;
+ }
+ }
+ return false;
+}
+
static void __init spectre_v2_select_mitigation(void)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@@ -213,6 +231,24 @@ static void __init spectre_v2_select_mitigation(void)

spectre_v2_enabled = mode;
pr_info("%s\n", spectre_v2_strings[mode]);
+
+ /*
+ * If neither SMEP or KPTI are available, there is a risk of
+ * hitting userspace addresses in the RSB after a context switch
+ * from a shallow call stack to a deeper one. To prevent this fill
+ * the entire RSB, even when using IBRS.
+ *
+ * Skylake era CPUs have a separate issue with *underflow* of the
+ * RSB, when they will predict 'ret' targets from the generic BTB.
+ * The proper mitigation for this is IBRS. If IBRS is not supported
+ * or deactivated in favour of retpolines the RSB fill on context
+ * switch is required.
+ */
+ if ((!boot_cpu_has(X86_FEATURE_PTI) &&
+ !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
+ setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
+ pr_info("Filling RSB on context switch\n");
+ }
}

#undef pr_fmt
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 05459ad3db46..d0e69769abfd 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -21,7 +21,6 @@ struct cpuid_bit {
static const struct cpuid_bit cpuid_bits[] = {
{ X86_FEATURE_APERFMPERF, CPUID_ECX, 0, 0x00000006, 0 },
{ X86_FEATURE_EPB, CPUID_ECX, 3, 0x00000006, 0 },
- { X86_FEATURE_INTEL_PT, CPUID_EBX, 25, 0x00000007, 0 },
{ X86_FEATURE_AVX512_4VNNIW, CPUID_EDX, 2, 0x00000007, 0 },
{ X86_FEATURE_AVX512_4FMAPS, CPUID_EDX, 3, 0x00000007, 0 },
{ X86_FEATURE_CAT_L3, CPUID_EBX, 1, 0x00000010, 0 },
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 47388f0c0e59..af6f2f9c6a26 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -21,10 +21,14 @@ extern struct range pfn_mapped[E820_MAX_ENTRIES];

static p4d_t tmp_p4d_table[PTRS_PER_P4D] __initdata __aligned(PAGE_SIZE);

-static __init void *early_alloc(size_t size, int nid)
+static __init void *early_alloc(size_t size, int nid, bool panic)
{
- return memblock_virt_alloc_try_nid_nopanic(size, size,
- __pa(MAX_DMA_ADDRESS), BOOTMEM_ALLOC_ACCESSIBLE, nid);
+ if (panic)
+ return memblock_virt_alloc_try_nid(size, size,
+ __pa(MAX_DMA_ADDRESS), BOOTMEM_ALLOC_ACCESSIBLE, nid);
+ else
+ return memblock_virt_alloc_try_nid_nopanic(size, size,
+ __pa(MAX_DMA_ADDRESS), BOOTMEM_ALLOC_ACCESSIBLE, nid);
}

static void __init kasan_populate_pmd(pmd_t *pmd, unsigned long addr,
@@ -38,14 +42,14 @@ static void __init kasan_populate_pmd(pmd_t *pmd, unsigned long addr,
if (boot_cpu_has(X86_FEATURE_PSE) &&
((end - addr) == PMD_SIZE) &&
IS_ALIGNED(addr, PMD_SIZE)) {
- p = early_alloc(PMD_SIZE, nid);
+ p = early_alloc(PMD_SIZE, nid, false);
if (p && pmd_set_huge(pmd, __pa(p), PAGE_KERNEL))
return;
else if (p)
memblock_free(__pa(p), PMD_SIZE);
}

- p = early_alloc(PAGE_SIZE, nid);
+ p = early_alloc(PAGE_SIZE, nid, true);
pmd_populate_kernel(&init_mm, pmd, p);
}

@@ -57,7 +61,7 @@ static void __init kasan_populate_pmd(pmd_t *pmd, unsigned long addr,
if (!pte_none(*pte))
continue;

- p = early_alloc(PAGE_SIZE, nid);
+ p = early_alloc(PAGE_SIZE, nid, true);
entry = pfn_pte(PFN_DOWN(__pa(p)), PAGE_KERNEL);
set_pte_at(&init_mm, addr, pte, entry);
} while (pte++, addr += PAGE_SIZE, addr != end);
@@ -75,14 +79,14 @@ static void __init kasan_populate_pud(pud_t *pud, unsigned long addr,
if (boot_cpu_has(X86_FEATURE_GBPAGES) &&
((end - addr) == PUD_SIZE) &&
IS_ALIGNED(addr, PUD_SIZE)) {
- p = early_alloc(PUD_SIZE, nid);
+ p = early_alloc(PUD_SIZE, nid, false);
if (p && pud_set_huge(pud, __pa(p), PAGE_KERNEL))
return;
else if (p)
memblock_free(__pa(p), PUD_SIZE);
}

- p = early_alloc(PAGE_SIZE, nid);
+ p = early_alloc(PAGE_SIZE, nid, true);
pud_populate(&init_mm, pud, p);
}

@@ -101,7 +105,7 @@ static void __init kasan_populate_p4d(p4d_t *p4d, unsigned long addr,
unsigned long next;

if (p4d_none(*p4d)) {
- void *p = early_alloc(PAGE_SIZE, nid);
+ void *p = early_alloc(PAGE_SIZE, nid, true);

p4d_populate(&init_mm, p4d, p);
}
@@ -122,7 +126,7 @@ static void __init kasan_populate_pgd(pgd_t *pgd, unsigned long addr,
unsigned long next;

if (pgd_none(*pgd)) {
- p = early_alloc(PAGE_SIZE, nid);
+ p = early_alloc(PAGE_SIZE, nid, true);
pgd_populate(&init_mm, pgd, p);
}

diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index bae807eb2933..853291714ae0 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -31,11 +31,17 @@
#else
#define MODULE_RANDSTRUCT_PLUGIN
#endif
+#ifdef RETPOLINE
+#define MODULE_VERMAGIC_RETPOLINE "retpoline "
+#else
+#define MODULE_VERMAGIC_RETPOLINE ""
+#endif

#define VERMAGIC_STRING \
UTS_RELEASE " " \
MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT \
MODULE_VERMAGIC_MODULE_UNLOAD MODULE_VERMAGIC_MODVERSIONS \
MODULE_ARCH_VERMAGIC \
- MODULE_RANDSTRUCT_PLUGIN
+ MODULE_RANDSTRUCT_PLUGIN \
+ MODULE_VERMAGIC_RETPOLINE

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index e63af4e19382..6bed45dc2cb1 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -270,12 +270,18 @@ else
objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
endif

+ifdef CONFIG_MODVERSIONS
+objtool_o = $(@D)/.tmp_$(@F)
+else
+objtool_o = $(@)
+endif
+
# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
# 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
cmd_objtool = $(if $(patsubst y%,, \
$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
- $(__objtool_obj) $(objtool_args) "$(@)";)
+ $(__objtool_obj) $(objtool_args) "$(objtool_o)";)
objtool_obj = $(if $(patsubst y%,, \
$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
$(__objtool_obj))
@@ -291,15 +297,15 @@ objtool_dep = $(objtool_obj) \
define rule_cc_o_c
$(call echo-cmd,checksrc) $(cmd_checksrc) \
$(call cmd_and_fixdep,cc_o_c) \
- $(cmd_modversions_c) \
$(call echo-cmd,objtool) $(cmd_objtool) \
+ $(cmd_modversions_c) \
$(call echo-cmd,record_mcount) $(cmd_record_mcount)
endef

define rule_as_o_S
$(call cmd_and_fixdep,as_o_S) \
- $(cmd_modversions_S) \
- $(call echo-cmd,objtool) $(cmd_objtool)
+ $(call echo-cmd,objtool) $(cmd_objtool) \
+ $(cmd_modversions_S)
endef

# List module undefined symbols (or empty line if not enabled)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 24460155c82c..c1c338661699 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -26,6 +26,7 @@
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
+#include <errno.h>

#include "elf.h"
#include "warn.h"
@@ -358,7 +359,8 @@ struct elf *elf_open(const char *name, int flags)

elf->fd = open(name, flags);
if (elf->fd == -1) {
- perror("open");
+ fprintf(stderr, "objtool: Can't open '%s': %s\n",
+ name, strerror(errno));
goto err;
}

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