diff options
| author | Thomas Gleixner | 2017-12-15 20:35:11 +0100 |
|---|---|---|
| committer | Ingo Molnar | 2017-12-23 21:13:01 +0100 |
| commit | 9f5cb6b32d9e0a3a7453222baaf15664d92adbf2 (patch) | |
| tree | 0440d750b55a764fcfbdebbecf8e065dd8dadb38 /tools | |
| parent | a4b51ef6552c704764684cef7e753162dc87c5fa (diff) | |
x86/ldt: Make the LDT mapping RO
Now that the LDT mapping is in a known area when PAGE_TABLE_ISOLATION is
enabled its a primary target for attacks, if a user space interface fails
to validate a write address correctly. That can never happen, right?
The SDM states:
If the segment descriptors in the GDT or an LDT are placed in ROM, the
processor can enter an indefinite loop if software or the processor
attempts to update (write to) the ROM-based segment descriptors. To
prevent this problem, set the accessed bits for all segment descriptors
placed in a ROM. Also, remove operating-system or executive code that
attempts to modify segment descriptors located in ROM.
So its a valid approach to set the ACCESS bit when setting up the LDT entry
and to map the table RO. Fixup the selftest so it can handle that new mode.
Remove the manual ACCESS bit setter in set_tls_desc() as this is now
pointless. Folded the patch from Peter Ziljstra.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/testing/selftests/x86/ldt_gdt.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c index 0304ffb714f2..1aef72df20a1 100644 --- a/tools/testing/selftests/x86/ldt_gdt.c +++ b/tools/testing/selftests/x86/ldt_gdt.c @@ -122,8 +122,7 @@ static void check_valid_segment(uint16_t index, int ldt, * NB: Different Linux versions do different things with the * accessed bit in set_thread_area(). */ - if (ar != expected_ar && - (ldt || ar != (expected_ar | AR_ACCESSED))) { + if (ar != expected_ar && ar != (expected_ar | AR_ACCESSED)) { printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n", (ldt ? "LDT" : "GDT"), index, ar, expected_ar); nerrs++; |