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authorPeter Zijlstra <peterz@infradead.org>2019-07-08 15:55:30 -0500
committerThomas Gleixner <tglx@linutronix.de>2019-07-09 22:39:15 +0200
commitecc606103837b98a2b665e8f14e533a6c72bbdc0 (patch)
tree13a82b9c7c38c22bc2a6fe14dba882076dc13134 /arch
parent1cbec37b3f9cff074a67bef4fc34b30a09958a0a (diff)
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x86/alternatives: Fix int3_emulate_call() selftest stack corruption
KASAN shows the following splat during boot: BUG: KASAN: unknown-crash in unwind_next_frame+0x3f6/0x490 Read of size 8 at addr ffffffff84007db0 by task swapper/0 CPU: 0 PID: 0 Comm: swapper Tainted: G T 5.2.0-rc6-00013-g7457c0d #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 Call Trace: dump_stack+0x19/0x1b print_address_description+0x1b0/0x2b2 __kasan_report+0x10f/0x171 kasan_report+0x12/0x1c __asan_load8+0x54/0x81 unwind_next_frame+0x3f6/0x490 unwind_next_frame+0x1b/0x23 arch_stack_walk+0x68/0xa5 stack_trace_save+0x7b/0xa0 save_trace+0x3c/0x93 mark_lock+0x1ef/0x9b1 lock_acquire+0x122/0x221 __mutex_lock+0xb6/0x731 mutex_lock_nested+0x16/0x18 _vm_unmap_aliases+0x141/0x183 vm_unmap_aliases+0x14/0x16 change_page_attr_set_clr+0x15e/0x2f2 set_memory_4k+0x2a/0x2c check_bugs+0x11fd/0x1298 start_kernel+0x793/0x7eb x86_64_start_reservations+0x55/0x76 x86_64_start_kernel+0x87/0xaa secondary_startup_64+0xa4/0xb0 Memory state around the buggy address: ffffffff84007c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 ffffffff84007d00: f1 00 00 00 00 00 00 00 00 00 f2 f2 f2 f3 f3 f3 >ffffffff84007d80: f3 79 be 52 49 79 be 00 00 00 00 00 00 00 00 f1 It turns out that int3_selftest() is corrupting the stack. The problem is that the KASAN-ified version of int3_magic() is much less trivial than the C code appears. It clobbers several unexpected registers. So when the selftest's INT3 is converted to an emulated call to int3_magic(), the registers are clobbered and Bad Things happen when the function returns. Fix this by converting int3_magic() to the trivial ASM function it should be, avoiding all calling convention issues. Also add ASM_CALL_CONSTRAINT to the INT3 ASM, since it contains a 'CALL'. [peterz: cribbed changelog from josh] Fixes: 7457c0da024b ("x86/alternatives: Add int3_emulate_call() selftest") Reported-by: kernel test robot <rong.a.chen@intel.com> Debugged-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Link: https://lkml.kernel.org/r/20190709125744.GB3402@hirez.programming.kicks-ass.net
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/alternative.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 99ef8b6f9a1a..ccd32013c47a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -625,10 +625,23 @@ extern struct paravirt_patch_site __start_parainstructions[],
*
* See entry_{32,64}.S for more details.
*/
-static void __init int3_magic(unsigned int *ptr)
-{
- *ptr = 1;
-}
+
+/*
+ * We define the int3_magic() function in assembly to control the calling
+ * convention such that we can 'call' it from assembly.
+ */
+
+extern void int3_magic(unsigned int *ptr); /* defined in asm */
+
+asm (
+" .pushsection .init.text, \"ax\", @progbits\n"
+" .type int3_magic, @function\n"
+"int3_magic:\n"
+" movl $1, (%" _ASM_ARG1 ")\n"
+" ret\n"
+" .size int3_magic, .-int3_magic\n"
+" .popsection\n"
+);
extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
@@ -676,7 +689,9 @@ static void __init int3_selftest(void)
"int3_selftest_ip:\n\t"
__ASM_SEL(.long, .quad) " 1b\n\t"
".popsection\n\t"
- : : __ASM_SEL_RAW(a, D) (&val) : "memory");
+ : ASM_CALL_CONSTRAINT
+ : __ASM_SEL_RAW(a, D) (&val)
+ : "memory");
BUG_ON(val != 1);