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authorBorislav Petkov <bp@suse.de>2018-01-12 21:55:29 +0100
committerBorislav Petkov <bp@suse.de>2018-01-12 21:55:38 +0100
commit39e8523ab1513e3a037c81e742dd900e969cf22f (patch)
treea3cea1cd18e12c11e90b49fe42aa124d2b23829f
parent39afc3bbbcb14008cff54c148a07e0a4f0038c7e (diff)
x86/entry/64: Create a per-CPU SYSCALL entry trampoline
(bsc#1068032 CVE-2017-5754). suse-commit: 8342aabecb4645621f68553598b779741fdee45d
-rw-r--r--arch/x86/entry/entry_64.S58
-rw-r--r--arch/x86/include/asm/fixmap.h2
-rw-r--r--arch/x86/kernel/asm-offsets.c1
-rw-r--r--arch/x86/kernel/cpu/common.c15
-rw-r--r--arch/x86/kernel/vmlinux.lds.S9
5 files changed, 84 insertions, 1 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index bd4b677932bb..24224771bea5 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -135,6 +135,64 @@ END(native_usergs_sysret64)
* with them due to bugs in both AMD and Intel CPUs.
*/
+ .pushsection .entry_trampoline, "ax"
+
+/*
+ * The code in here gets remapped into cpu_entry_area's trampoline. This means
+ * that the assembler and linker have the wrong idea as to where this code
+ * lives (and, in fact, it's mapped more than once, so it's not even at a
+ * fixed address). So we can't reference any symbols outside the entry
+ * trampoline and expect it to work.
+ *
+ * Instead, we carefully abuse %rip-relative addressing.
+ * _entry_trampoline(%rip) refers to the start of the remapped) entry
+ * trampoline. We can thus find cpu_entry_area with this macro:
+ */
+
+#define CPU_ENTRY_AREA \
+ _entry_trampoline - CPU_ENTRY_AREA_entry_trampoline(%rip)
+
+/* The top word of the SYSENTER stack is hot and is usable as scratch space. */
+#define RSP_SCRATCH CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + \
+ SIZEOF_SYSENTER_stack - 8 + CPU_ENTRY_AREA
+
+ENTRY(entry_SYSCALL_64_trampoline)
+ UNWIND_HINT_EMPTY
+ swapgs
+
+ /* Stash the user RSP. */
+ movq %rsp, RSP_SCRATCH
+
+ /* Load the top of the task stack into RSP */
+ movq CPU_ENTRY_AREA_tss + TSS_sp1 + CPU_ENTRY_AREA, %rsp
+
+ /* Start building the simulated IRET frame. */
+ pushq $__USER_DS /* pt_regs->ss */
+ pushq RSP_SCRATCH /* pt_regs->sp */
+ pushq %r11 /* pt_regs->flags */
+ pushq $__USER_CS /* pt_regs->cs */
+ pushq %rcx /* pt_regs->ip */
+
+ /*
+ * x86 lacks a near absolute jump, and we can't jump to the real
+ * entry text with a relative jump. We could push the target
+ * address and then use retq, but this destroys the pipeline on
+ * many CPUs (wasting over 20 cycles on Sandy Bridge). Instead,
+ * spill RDI and restore it in a second-stage trampoline.
+ */
+ pushq %rdi
+ movq $entry_SYSCALL_64_stage2, %rdi
+ jmp *%rdi
+END(entry_SYSCALL_64_trampoline)
+
+ .popsection
+
+ENTRY(entry_SYSCALL_64_stage2)
+ UNWIND_HINT_EMPTY
+ popq %rdi
+ jmp entry_SYSCALL_64_after_hwframe
+END(entry_SYSCALL_64_stage2)
+
ENTRY(entry_SYSCALL_64)
UNWIND_HINT_EMPTY
/*
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index c8aaf4b56699..17be88e73c92 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -61,6 +61,8 @@ struct cpu_entry_area {
* of the TSS region.
*/
struct tss_struct tss;
+
+ char entry_trampoline[PAGE_SIZE];
};
#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE)
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index f765c3253ec3..822be00c85ff 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -100,4 +100,5 @@ void common(void) {
/* Layout info for cpu_entry_area */
OFFSET(CPU_ENTRY_AREA_tss, cpu_entry_area, tss);
+ OFFSET(CPU_ENTRY_AREA_entry_trampoline, cpu_entry_area, entry_trampoline);
}
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 53285de7d22e..f57fc6ad4ba5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -468,6 +468,8 @@ DEFINE_PER_CPU(struct cpu_entry_area *, cpu_entry_area);
static inline void setup_cpu_entry_area(int cpu)
{
#ifdef CONFIG_X86_64
+ extern char _entry_trampoline[];
+
/* On 64-bit systems, we use a read-only fixmap GDT. */
pgprot_t gdt_prot = PAGE_KERNEL_RO;
#else
@@ -514,6 +516,11 @@ static inline void setup_cpu_entry_area(int cpu)
#ifdef CONFIG_X86_32
this_cpu_write(cpu_entry_area, get_cpu_entry_area(cpu));
#endif
+
+#ifdef CONFIG_X86_64
+ __set_fixmap(get_cpu_entry_area_index(cpu, entry_trampoline),
+ __pa_symbol(_entry_trampoline), PAGE_KERNEL_RX);
+#endif
}
/* Load the original GDT from the per-cpu structure */
@@ -1380,10 +1387,16 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
+ extern char _entry_trampoline[];
+ extern char entry_SYSCALL_64_trampoline[];
+
int cpu = smp_processor_id();
+ unsigned long SYSCALL64_entry_trampoline =
+ (unsigned long)get_cpu_entry_area(cpu)->entry_trampoline +
+ (entry_SYSCALL_64_trampoline - _entry_trampoline);
wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
- wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
+ wrmsrl(MSR_LSTAR, SYSCALL64_entry_trampoline);
#ifdef CONFIG_IA32_EMULATION
wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index f05f00acac89..423aa36f0150 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -106,6 +106,15 @@ SECTIONS
SOFTIRQENTRY_TEXT
*(.fixup)
*(.gnu.warning)
+
+#ifdef CONFIG_X86_64
+ . = ALIGN(PAGE_SIZE);
+ _entry_trampoline = .;
+ *(.entry_trampoline)
+ . = ALIGN(PAGE_SIZE);
+ ASSERT(. - _entry_trampoline == PAGE_SIZE, "entry trampoline is too big");
+#endif
+
/* End of text section */
_etext = .;
} :text = 0x9090