x86/unwind/orc: Unwind ftrace trampolines with correct ORC entry

commit fc2e426b1161761561624ebd43ce8c8d2fa058da upstream.

When meeting ftrace trampolines in ORC unwinding, unwinder uses address
of ftrace_{regs_}call address to find the ORC entry, which gets next frame at
sp+176.

If there is an IRQ hitting at sub $0xa8,%rsp, the next frame should be
sp+8 instead of 176. It makes unwinder skip correct frame and throw
warnings such as "wrong direction" or "can't access registers", etc,
depending on the content of the incorrect frame address.

By adding the base address ftrace_{regs_}caller with the offset
*ip - ops->trampoline*, we can get the correct address to find the ORC entry.

Also change "caller" to "tramp_addr" to make variable name conform to
its content.

[ mingo: Clarified the changelog a bit. ]

Fixes: 6be7fa3c74d1 ("ftrace, orc, x86: Handle ftrace dynamically allocated trampolines")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220819084334.244016-1-chenzhongjin@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index c451d5f6422f64dac558b8c8068bb9b39a2987a5..cc071c4c65240b0192e3f323d7c6750d7557b2c0 100644 (file)
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -93,22 +93,27 @@ static struct orc_entry *orc_find(unsigned long ip);
 static struct orc_entry *orc_ftrace_find(unsigned long ip)
 {
        struct ftrace_ops *ops;
-       unsigned long caller;
+       unsigned long tramp_addr, offset;
 
        ops = ftrace_ops_trampoline(ip);
        if (!ops)
                return NULL;
 
+       /* Set tramp_addr to the start of the code copied by the trampoline */
        if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
-               caller = (unsigned long)ftrace_regs_call;
+               tramp_addr = (unsigned long)ftrace_regs_caller;
        else
-               caller = (unsigned long)ftrace_call;
+               tramp_addr = (unsigned long)ftrace_caller;
+
+       /* Now place tramp_addr to the location within the trampoline ip is at */
+       offset = ip - ops->trampoline;
+       tramp_addr += offset;
 
        /* Prevent unlikely recursion */
-       if (ip == caller)
+       if (ip == tramp_addr)
                return NULL;
 
-       return orc_find(caller);
+       return orc_find(tramp_addr);
 }
 #else
 static struct orc_entry *orc_ftrace_find(unsigned long ip)