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x86/kprobes: Prohibit kprobing on INT and UD

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Both INT (INT n, INT1, INT3, INTO) and UD (UD0, UD1, UD2) serve special
purposes in the kernel, e.g., INT3 is used by KGDB and UD2 is involved
in LLVM-KCFI instrumentation. At the same time, attaching kprobes on
these instructions (particularly UD) will pollute the stack trace dumped
in the kernel ring buffer, since the exception is triggered in the copy
buffer rather than the original location.

Check for INT and UD in can_probe and reject any kprobes trying to
attach to these instructions.

Link: https://lore.kernel.org/all/20240204031300.830475-3-jinghao7@illinois.edu/

Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinghao Jia <jinghao7@illinois.edu>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
This commit is contained in:
Jinghao Jia 2024-03-07 00:26:01 +09:00 committed by Masami Hiramatsu (Google)
parent e4778a0ef3
commit e884edbb84
1 changed files with 39 additions and 9 deletions
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48
arch/x86/kernel/kprobes/core.c
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@ -252,7 +252,28 @@ unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long add
return __recover_probed_insn(buf, addr);
}
/* Check if paddr is at an instruction boundary */
/* Check if insn is INT or UD */
static inline bool is_exception_insn(struct insn *insn)
{
/* UD uses 0f escape */
if (insn->opcode.bytes[0] == 0x0f) {
/* UD0 / UD1 / UD2 */
return insn->opcode.bytes[1] == 0xff ||
insn->opcode.bytes[1] == 0xb9 ||
insn->opcode.bytes[1] == 0x0b;
}
/* INT3 / INT n / INTO / INT1 */
return insn->opcode.bytes[0] == 0xcc ||
insn->opcode.bytes[0] == 0xcd ||
insn->opcode.bytes[0] == 0xce ||
insn->opcode.bytes[0] == 0xf1;
}
/*
* Check if paddr is at an instruction boundary and that instruction can
* be probed
*/
static bool can_probe(unsigned long paddr)
{
unsigned long addr, __addr, offset = 0;
@ -291,6 +312,22 @@ static bool can_probe(unsigned long paddr)
#endif
addr += insn.length;
}
/* Check if paddr is at an instruction boundary */
if (addr != paddr)
return false;
__addr = recover_probed_instruction(buf, addr);
if (!__addr)
return false;
if (insn_decode_kernel(&insn, (void *)__addr) < 0)
return false;
/* INT and UD are special and should not be kprobed */
if (is_exception_insn(&insn))
return false;
if (IS_ENABLED(CONFIG_CFI_CLANG)) {
/*
* The compiler generates the following instruction sequence
@ -305,13 +342,6 @@ static bool can_probe(unsigned long paddr)
* Also, these movl and addl are used for showing expected
* type. So those must not be touched.
*/
__addr = recover_probed_instruction(buf, addr);
if (!__addr)
return false;
if (insn_decode_kernel(&insn, (void *)__addr) < 0)
return false;
if (insn.opcode.value == 0xBA)
offset = 12;
else if (insn.opcode.value == 0x3)
@ -325,7 +355,7 @@ static bool can_probe(unsigned long paddr)
}
out:
return (addr == paddr);
return true;
}
/* If x86 supports IBT (ENDBR) it must be skipped. */