Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
x86/alternative: Refactor INT3 call emulation selftest
The INT3 call emulation selftest is a bit fragile as it relies on the
compiler not inserting any extra instructions before the
int3_selftest_ip() definition.
Also, the int3_selftest_ip() symbol overlaps with the int3_selftest
symbol(), which can confuse objtool.
Fix those issues by slightly reworking the functionality and moving
int3_selftest_ip() to a separate asm function. While at it, improve the
naming.
Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
+28
-23
+28
-23
arch/x86/kernel/alternative.c
+28
-23
arch/x86/kernel/alternative.c
···
2244
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* See entry_{32,64}.S for more details.
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*/
2246
2246
2247
-
/*
2248
-
* We define the int3_magic() function in assembly to control the calling
2249
-
* convention such that we can 'call' it from assembly.
2250
-
*/
2251
-
2252
-
extern void int3_magic(unsigned int *ptr); /* defined in asm */
2247
+
extern void int3_selftest_asm(unsigned int *ptr);
2253
2248
2254
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asm (
2255
2250
" .pushsection .init.text, \"ax\", @progbits\n"
2256
-
" .type int3_magic, @function\n"
2257
-
"int3_magic:\n"
2251
+
" .type int3_selftest_asm, @function\n"
2252
+
"int3_selftest_asm:\n"
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ANNOTATE_NOENDBR
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-
" movl $1, (%" _ASM_ARG1 ")\n"
2254
+
/*
2255
+
* INT3 padded with NOP to CALL_INSN_SIZE. The INT3 triggers an
2256
+
* exception, then the int3_exception_nb notifier emulates a call to
2257
+
* int3_selftest_callee().
2258
+
*/
2259
+
" int3; nop; nop; nop; nop\n"
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ASM_RET
2261
-
" .size int3_magic, .-int3_magic\n"
2261
+
" .size int3_selftest_asm, . - int3_selftest_asm\n"
2262
+
" .popsection\n"
2263
+
);
2264
+
2265
+
extern void int3_selftest_callee(unsigned int *ptr);
2266
+
2267
+
asm (
2268
+
" .pushsection .init.text, \"ax\", @progbits\n"
2269
+
" .type int3_selftest_callee, @function\n"
2270
+
"int3_selftest_callee:\n"
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+
ANNOTATE_NOENDBR
2272
+
" movl $0x1234, (%" _ASM_ARG1 ")\n"
2273
+
ASM_RET
2274
+
" .size int3_selftest_callee, . - int3_selftest_callee\n"
2262
2275
" .popsection\n"
2263
2276
);
2264
2277
···
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static int __init
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int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
2282
2269
{
2283
-
unsigned long selftest = (unsigned long)&int3_selftest_ip;
2270
+
unsigned long selftest = (unsigned long)&int3_selftest_asm;
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struct die_args *args = data;
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struct pt_regs *regs = args->regs;
2286
2273
···
2295
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if (regs->ip - INT3_INSN_SIZE != selftest)
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return NOTIFY_DONE;
2297
2284
2298
-
int3_emulate_call(regs, (unsigned long)&int3_magic);
2285
+
int3_emulate_call(regs, (unsigned long)&int3_selftest_callee);
2299
2286
return NOTIFY_STOP;
2300
2287
}
2301
2288
···
2311
2298
BUG_ON(register_die_notifier(&int3_exception_nb));
2312
2299
2313
2300
/*
2314
-
* Basically: int3_magic(&val); but really complicated :-)
2315
-
*
2316
-
* INT3 padded with NOP to CALL_INSN_SIZE. The int3_exception_nb
2317
-
* notifier above will emulate CALL for us.
2301
+
* Basically: int3_selftest_callee(&val); but really complicated :-)
2318
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*/
2319
-
asm volatile ("int3_selftest_ip:\n\t"
2320
-
ANNOTATE_NOENDBR
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-
" int3; nop; nop; nop; nop\n\t"
2322
-
: ASM_CALL_CONSTRAINT
2323
-
: __ASM_SEL_RAW(a, D) (&val)
2324
-
: "memory");
2303
+
int3_selftest_asm(&val);
2325
2304
2326
-
BUG_ON(val != 1);
2305
+
BUG_ON(val != 0x1234);
2327
2306
2328
2307
unregister_die_notifier(&int3_exception_nb);
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2308
}