This is a note to let you know that I've just added the patch titled
x86/ibt,ftrace: Make function-graph play nice
to the 5.15-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-ibt-ftrace-make-function-graph-play-nice.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Fri Aug 19 01:18:09 PM CEST 2022
From: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Date: Tue, 16 Aug 2022 05:26:57 -0300
Subject: x86/ibt,ftrace: Make function-graph play nice
To: stable@xxxxxxxxxxxxxxx
Cc: paul.gortmaker@xxxxxxxxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxx, peterz@xxxxxxxxxxxxx, bp@xxxxxxx, jpoimboe@xxxxxxxxxx, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Message-ID: <20220816082658.172387-2-cascardo@xxxxxxxxxxxxx>
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit e52fc2cf3f662828cc0d51c4b73bed73ad275fce upstream.
Return trampoline must not use indirect branch to return; while this
preserves the RSB, it is fundamentally incompatible with IBT. Instead
use a retpoline like ROP gadget that defeats IBT while not unbalancing
the RSB.
And since ftrace_stub is no longer a plain RET, don't use it to copy
from. Since RET is a trivial instruction, poke it directly.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220308154318.347296408@xxxxxxxxxxxxx
[cascardo: remove ENDBR]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/ftrace.c | 9 ++-------
arch/x86/kernel/ftrace_64.S | 19 +++++++++++++++----
2 files changed, 17 insertions(+), 11 deletions(-)
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -322,12 +322,12 @@ create_trampoline(struct ftrace_ops *ops
unsigned long offset;
unsigned long npages;
unsigned long size;
- unsigned long retq;
unsigned long *ptr;
void *trampoline;
void *ip;
/* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
+ unsigned const char retq[] = { RET_INSN_OPCODE, INT3_INSN_OPCODE };
union ftrace_op_code_union op_ptr;
int ret;
@@ -365,12 +365,7 @@ create_trampoline(struct ftrace_ops *ops
goto fail;
ip = trampoline + size;
-
- /* The trampoline ends with ret(q) */
- retq = (unsigned long)ftrace_stub;
- ret = copy_from_kernel_nofault(ip, (void *)retq, RET_SIZE);
- if (WARN_ON(ret < 0))
- goto fail;
+ memcpy(ip, retq, RET_SIZE);
/* No need to test direct calls on created trampolines */
if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -181,7 +181,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L
/*
* This is weak to keep gas from relaxing the jumps.
- * It is also used to copy the RET for trampolines.
*/
SYM_INNER_LABEL_ALIGN(ftrace_stub, SYM_L_WEAK)
UNWIND_HINT_FUNC
@@ -335,7 +334,7 @@ SYM_FUNC_START(ftrace_graph_caller)
SYM_FUNC_END(ftrace_graph_caller)
SYM_FUNC_START(return_to_handler)
- subq $24, %rsp
+ subq $16, %rsp
/* Save the return values */
movq %rax, (%rsp)
@@ -347,7 +346,19 @@ SYM_FUNC_START(return_to_handler)
movq %rax, %rdi
movq 8(%rsp), %rdx
movq (%rsp), %rax
- addq $24, %rsp
- JMP_NOSPEC rdi
+
+ addq $16, %rsp
+ /*
+ * Jump back to the old return address. This cannot be JMP_NOSPEC rdi
+ * since IBT would demand that contain ENDBR, which simply isn't so for
+ * return addresses. Use a retpoline here to keep the RSB balanced.
+ */
+ ANNOTATE_INTRA_FUNCTION_CALL
+ call .Ldo_rop
+ int3
+.Ldo_rop:
+ mov %rdi, (%rsp)
+ UNWIND_HINT_FUNC
+ RET
SYM_FUNC_END(return_to_handler)
#endif
Patches currently in stable-queue which might be from cascardo@xxxxxxxxxxxxx are
queue-5.15/x86-ftrace-use-alternative-ret-encoding.patch
queue-5.15/revert-x86-ftrace-use-alternative-ret-encoding.patch
queue-5.15/net_sched-cls_route-disallow-handle-of-0.patch
queue-5.15/x86-ibt-ftrace-make-function-graph-play-nice.patch
