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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Ping#3: [PATCH v3] x86/HVM: don't #GP/#SS on wrapping virt->linear translations
>>> On 04.12.17 at 17:39, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 04/12/17 10:16, Jan Beulich wrote:
>>>>> On 25.08.17 at 16:59, wrote:
>>>>>> On 10.08.17 at 09:19, <JBeulich@xxxxxxxx> wrote:
>>>>>>> On 10.07.17 at 12:39, <JBeulich@xxxxxxxx> wrote:
>>>>> Real hardware wraps silently in most cases, so we should behave the
>>>>> same. Also split real and VM86 mode handling, as the latter really
>>>>> ought to have limit checks applied.
>>>>>
>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>> ---
>>>>> v3: Restore 32-bit wrap check for AMD.
>>>>> v2: Extend to non-64-bit modes. Reduce 64-bit check to a single
>>>>> is_canonical_address() invocation.
>> Same here - I think I've been carrying this for long enough.
>
> I'm not sure what to say. I'm not comfortable taking this change
> without a regression test in place, which also serves to demonstrate the
> correctness of the change.
>
> Its simply a matter of time, not any other objection to the change.
Well, I had sent you a tentative XTF test long ago (non-publicly
at the time, I believe). Here it is again. I'll send a second change
in a minute, which iirc is necessary as prereq to the one here.
Jan
add split memory access tests
Add tests to verify that accesses crossing the upper address boundary
are being handled similarly with and without the emulator involved.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Use FS overrides. Add 64-bit and PV tests. Remove stray '-s from
log messages. Add "X" (ex_record_fault_eax) constraints.
--- /dev/null
+++ b/tests/split-access/Makefile
@@ -0,0 +1,9 @@
+include $(ROOT)/build/common.mk
+
+NAME := split-access
+CATEGORY := functional
+TEST-ENVS := $(ALL_ENVIRONMENTS)
+
+obj-perenv += main.o
+
+include $(ROOT)/build/gen.mk
--- /dev/null
+++ b/tests/split-access/main.c
@@ -0,0 +1,251 @@
+/**
+ * @file tests/split-access/main.c
+ * @ref test-split-access
+ *
+ * @page test-split-access split-access
+ *
+ * @todo Docs for test-split-access
+ *
+ * @see tests/split-access/main.c
+ */
+#include <xtf.h>
+
+#include <arch/decode.h>
+#include <arch/pagetable.h>
+
+const char test_title[] = "Split memory access insns";
+
+const void *volatile boundary = NULL;
+
+/* Keep the compiler from leveraging undefined behavior. */
+#define touch(x) ({ asm ( "" : "+g" (x) ); })
+
+void do_mov(bool force)
+{
+ const unsigned long *ptr = boundary;
+
+ touch(ptr);
+ for ( --ptr; ; )
+ {
+ unsigned long val;
+ exinfo_t fault = 0;
+
+ asm volatile ( "test %[fep], %[fep];"
+ "jz 1f;"
+ _ASM_XEN_FEP
+ "1: mov %%fs:%[src],%[dst]; 2:"
+ _ASM_EXTABLE_HANDLER(1b, 2b, ex_record_fault_eax)
+ : [dst] "=r" (val), "+a" (fault)
+ : [src] "m" (*ptr), [fep] "q" (force),
+ "X" (ex_record_fault_eax) );
+ if ( fault )
+ xtf_warning("Got %pe for %p\n", _p(fault), ptr);
+ else if ( val != *ptr )
+ xtf_failure("%lx != %lx for %p\n", val, *ptr, ptr);
+
+ touch(ptr);
+ if ( ptr == boundary )
+ break;
+
+ ptr = (void *)(long)ptr + 1;
+ }
+}
+
+void do_lfs(bool force)
+{
+ const struct __packed { unsigned long off; uint16_t sel; } *ptr = boundary;
+
+ touch(ptr);
+ for ( --ptr; ; )
+ {
+ unsigned long off;
+ exinfo_t fault = 0;
+
+ asm volatile ( "test %[fep], %[fep];"
+ "jz 1f;"
+ _ASM_XEN_FEP
+ "1: lfs %%fs:%[src],%[dst]; 2:"
+ _ASM_EXTABLE_HANDLER(1b, 2b, ex_record_fault_eax)
+ : [dst] "=r" (off), "+a" (fault)
+ : [src] "m" (*ptr), [fep] "q" (force),
+ "X" (ex_record_fault_eax) );
+ if ( fault )
+ xtf_warning("Got %pe for %p\n", _p(fault), ptr);
+ else if ( off != ptr->off )
+ xtf_failure("%lx != %lx for %p\n", off, ptr->off, ptr);
+
+ touch(ptr);
+ if ( ptr == boundary )
+ break;
+
+ ptr = (void *)(long)ptr + 1;
+ }
+}
+
+#ifdef CONFIG_HVM
+void do_lidt(bool force)
+{
+ const desc_ptr *ptr = boundary;
+
+ touch(ptr);
+ for ( --ptr; ; )
+ {
+ exinfo_t fault = 0;
+
+ asm volatile ( "test %[fep], %[fep];"
+ "jz 1f;"
+ _ASM_XEN_FEP
+ "1: lidt %%fs:%[src]; 2:"
+ _ASM_EXTABLE_HANDLER(1b, 2b, ex_record_fault_eax)
+ : "+a" (fault)
+ : [src] "m" (*ptr), [fep] "q" (force),
+ "X" (ex_record_fault_eax) );
+ if ( fault )
+ xtf_warning("Got %pe for %p\n", _p(fault), ptr);
+ else
+ asm volatile ( "lidt %0" :: "m" (idt_ptr) );
+
+ touch(ptr);
+ if ( ptr == boundary )
+ break;
+
+ ptr = (void *)(long)ptr + 1;
+ }
+}
+#endif
+
+#ifndef __x86_64__
+void do_bound(bool force)
+{
+ const struct { unsigned long lo, hi; } *ptr = boundary;
+
+ touch(ptr);
+ for ( --ptr; ; )
+ {
+ exinfo_t fault = 0;
+
+ asm volatile ( "test %[fep], %[fep];"
+ "jz 1f;"
+ _ASM_XEN_FEP
+ "1: bound %[off], %%fs:%[bnd]; 2:"
+ _ASM_EXTABLE_HANDLER(1b, 2b, ex_record_fault_eax)
+ : "+a" (fault)
+ : [bnd] "m" (*ptr), [off] "r" (0), [fep] "q" (force),
+ "X" (ex_record_fault_eax) );
+ if ( fault )
+ xtf_warning("Got %pe for %p\n", _p(fault), ptr);
+
+ touch(ptr);
+ if ( ptr == boundary )
+ break;
+
+ ptr = (void *)(long)ptr + 1;
+ }
+}
+#endif
+
+void run_tests(bool force)
+{
+ printk("Testing%s MOV\n", force ? " emulated" : "");
+ do_mov(force);
+
+ printk("Testing%s LFS\n", force ? " emulated" : "");
+ do_lfs(force);
+
+#ifdef CONFIG_HVM
+ printk("Testing%s LIDT\n", force ? " emulated" : "");
+ do_lidt(force);
+#endif
+
+#ifndef __x86_64__
+ printk("Testing%s BOUND\n", force ? " emulated" : "");
+ do_bound(force);
+#endif
+}
+
+void test_main(void)
+{
+#if defined(__x86_64__)
+ if ( !boundary )
+ {
+ asm volatile ( "push $0; pop %%fs" ::: "memory" );
+
+# if CONFIG_PAGING_LEVELS == 4
+ boundary = (void *)(1L << 47);
+# elif CONFIG_PAGING_LEVELS == 5
+ boundary = (void *)(1L << 56);
+# else
+# error Unknown 64-bit paging mode!
+# endif
+ printk("Testing at lower canonical boundary\n");
+ test_main();
+
+ boundary = NULL;
+ printk("Testing at upper address boundary\n");
+ }
+#elif defined(CONFIG_PV)
+ /* Shrink %fs limit to below the compat limit. */
+ static struct seg_desc32 __page_aligned_data desc[] = {
+ [1] = {
+ .limit0 = 0x4fff, .limit1 = 0xf, .g = 1,
+ .p = 1, .s = 1, .type = 3, .dpl = 1,
+ },
+ };
+ unsigned long frame = virt_to_mfn(desc);
+ int rc;
+
+ rc = hypercall_update_va_mapping((unsigned long)desc,
+ pte_from_gfn(frame,
+ _PAGE_PRESENT|_PAGE_AD),
+ 0);
+ if ( !rc )
+ rc = HYPERCALL2(int, __HYPERVISOR_set_gdt, &frame, ARRAY_SIZE(desc));
+ if ( rc )
+ {
+ xtf_error("Cannot set GDT entry: %d\n", rc);
+ return;
+ }
+
+ asm volatile ( "mov %1, %%fs; lsl %1, %0"
+ : "=r" (boundary)
+ : "r" (sizeof(*desc) | 1)
+ : "memory" );
+#else
+ /*
+ * To better tell actual hardware behavior, zap the mapping for the last
+ * (large) page below 4Gb. That'll make us see page faults on hardware
+ * when all segmentation checks pass, rather than observing #GP/#SS due to
+ * the emulator being invoked anyway due to accesses touching an unmapped
+ * MMIO range. This matches x86-64 behavior at the 2^^64 boundary.
+ */
+# if CONFIG_PAGING_LEVELS == 2
+ pse_l2_identmap[pse_l2_table_offset(~0UL)] = 0;
+# elif CONFIG_PAGING_LEVELS == 3
+ pae_l2_identmap[pae_l2_table_offset(~0UL)] = 0;
+# elif CONFIG_PAGING_LEVELS
+# error Unknown 32-bit paging mode!
+# endif
+
+ invlpg((void *)~0UL);
+ asm volatile ( "push %%ds; pop %%fs" ::: "memory" );
+#endif
+
+ run_tests(false);
+
+ if ( !xtf_has_fep )
+ xtf_skip("FEP support not detected - some tests will be skipped\n");
+ else
+ run_tests(true);
+
+ xtf_success(NULL);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
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