Patch "x86/kprobes: Fix optprobe optimization check with CONFIG_RETHUNK" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/kprobes: Fix optprobe optimization check with CONFIG_RETHUNK

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-kprobes-fix-optprobe-optimization-check-with-con.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5e1c0e63e98ffedb57bb62dc0183a44cb126f2ad
Author: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Date:   Mon Dec 19 23:35:19 2022 +0900

    x86/kprobes: Fix optprobe optimization check with CONFIG_RETHUNK
    
    [ Upstream commit 63dc6325ff41ee9e570bde705ac34a39c5dbeb44 ]
    
    Since the CONFIG_RETHUNK and CONFIG_SLS will use INT3 for stopping
    speculative execution after function return, kprobe jump optimization
    always fails on the functions with such INT3 inside the function body.
    (It already checks the INT3 padding between functions, but not inside
     the function)
    
    To avoid this issue, as same as kprobes, check whether the INT3 comes
    from kgdb or not, and if so, stop decoding and make it fail. The other
    INT3 will come from CONFIG_RETHUNK/CONFIG_SLS and those can be
    treated as a one-byte instruction.
    
    Fixes: e463a09af2f0 ("x86: Add straight-line-speculation mitigation")
    Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Link: https://lore.kernel.org/r/167146051929.1374301.7419382929328081706.stgit@devnote3
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 4299fc865732..3d6201492006 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -15,6 +15,7 @@
 #include <linux/extable.h>
 #include <linux/kdebug.h>
 #include <linux/kallsyms.h>
+#include <linux/kgdb.h>
 #include <linux/ftrace.h>
 #include <linux/objtool.h>
 #include <linux/pgtable.h>
@@ -272,19 +273,6 @@ 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)
 {
@@ -327,15 +315,15 @@ static int can_optimize(unsigned long paddr)
 		ret = insn_decode(&insn, (void *)recovered_insn, MAX_INSN_SIZE, INSN_MODE_KERN);
 		if (ret < 0)
 			return 0;
-
+#ifdef CONFIG_KGDB
 		/*
-		 * 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 there is a dynamically installed kgdb sw breakpoint,
+		 * this function should not be probed.
 		 */
-		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE)
-			return is_padding_int3(addr, paddr - offset + size) ? 1 : 0;
-
+		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
+		    kgdb_has_hit_break(addr))
+			return 0;
+#endif
 		/* Recover address */
 		insn.kaddr = (void *)addr;
 		insn.next_byte = (void *)(addr + insn.length);