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authorMasami Hiramatsu <mhiramat@kernel.org>2020-12-11 16:04:17 +0900
committerBorislav Petkov <bp@suse.de>2020-12-12 15:25:17 +0100
commit0d07c0ec4381f630c801539c79ad8dcc627f6e4a (patch)
treeca19541841b50372bb92d9ad2e3043a927d943f2
parent190113b4c6531c8e09b31d5235f9b5175cbb0f72 (diff)
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x86/kprobes: Fix optprobe to detect INT3 padding correctly
Commit 7705dc855797 ("x86/vmlinux: Use INT3 instead of NOP for linker fill bytes") changed the padding bytes between functions from NOP to INT3. However, when optprobe decodes a target function it finds INT3 and gives up the jump optimization. Instead of giving up any INT3 detection, check whether the rest of the bytes to the end of the function are INT3. If all of them are INT3, those come from the linker. In that case, continue the optprobe jump optimization. [ bp: Massage commit message. ] Fixes: 7705dc855797 ("x86/vmlinux: Use INT3 instead of NOP for linker fill bytes") Reported-by: Adam Zabrocki <pi3@pi3.com.pl> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/160767025681.3880685.16021570341428835411.stgit@devnote2
-rw-r--r--arch/x86/kernel/kprobes/opt.c22
1 files changed, 20 insertions, 2 deletions
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 041f0b50bc27..08eb23074f92 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -272,6 +272,19 @@ static int insn_is_indirect_jump(struct insn *insn)
return ret;
}
+static bool is_padding_int3(unsigned long addr, unsigned long eaddr)
+{
+ unsigned char ops;
+
+ for (; addr < eaddr; addr++) {
+ if (get_kernel_nofault(ops, (void *)addr) < 0 ||
+ ops != INT3_INSN_OPCODE)
+ return false;
+ }
+
+ return true;
+}
+
/* Decode whole function to ensure any instructions don't jump into target */
static int can_optimize(unsigned long paddr)
{
@@ -310,9 +323,14 @@ static int can_optimize(unsigned long paddr)
return 0;
kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
insn_get_length(&insn);
- /* Another subsystem puts a breakpoint */
+ /*
+ * In the case of detecting unknown breakpoint, this could be
+ * a padding INT3 between functions. Let's check that all the
+ * rest of the bytes are also INT3.
+ */
if (insn.opcode.bytes[0] == INT3_INSN_OPCODE)
- return 0;
+ return is_padding_int3(addr, paddr - offset + size) ? 1 : 0;
+
/* Recover address */
insn.kaddr = (void *)addr;
insn.next_byte = (void *)(addr + insn.length);