From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dan Carpenter <dan.carpenter@oracle.com>,
kernel-janitors@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Jiri Olsa <jolsa@kernel.org>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next 3/2] x86,rethook: Fix arch_rethook_trampoline() to generate a complete pt_regs
Date: Fri, 25 Mar 2022 12:40:12 +0100 [thread overview]
Message-ID: <20220325114012.GO8939@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <164818251899.2252200.7306353689206167903.stgit@devnote2>
You lost the regs->ss bit again..
Boot tested on tigerlake with IBT enabled -- passed the boot time
kretprobe selftests.
---
Subject: x86,rethook: Fix arch_rethook_trampoline() to generate a complete pt_regs
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri Mar 25 10:25:56 CET 2022
Currently arch_rethook_trampoline() generates an almost complete
pt_regs on-stack, everything except regs->ss that is, that currently
points to the fake return address, which is not a valid segment
descriptor.
Since interpretation of regs->[sb]p should be done in the context of
regs->ss, and we have code actually doing that (see
arch/x86/lib/insn-eval.c for instance), complete the job by also
pushing ss.
This ensures that anybody who does do look at regs->ss doesn't
mysteriously malfunction, avoiding much future pain.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/rethook.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)
--- a/arch/x86/kernel/rethook.c
+++ b/arch/x86/kernel/rethook.c
@@ -25,29 +25,31 @@ asm(
/* Push a fake return address to tell the unwinder it's a kretprobe. */
" pushq $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
- /* Save the 'sp - 8', this will be fixed later. */
+ " pushq $" __stringify(__KERNEL_DS) "\n"
+ /* Save the 'sp - 16', this will be fixed later. */
" pushq %rsp\n"
" pushfq\n"
SAVE_REGS_STRING
" movq %rsp, %rdi\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
- /* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
- " addq $8, %rsp\n"
+ /* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
+ " addq $16, %rsp\n"
" popfq\n"
#else
/* Push a fake return address to tell the unwinder it's a kretprobe. */
" pushl $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
- /* Save the 'sp - 4', this will be fixed later. */
+ " pushl %ss\n"
+ /* Save the 'sp - 8', this will be fixed later. */
" pushl %esp\n"
" pushfl\n"
SAVE_REGS_STRING
" movl %esp, %eax\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
- /* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
- " addl $4, %esp\n"
+ /* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
+ " addl $8, %esp\n"
" popfl\n"
#endif
ASM_RET
@@ -69,8 +71,8 @@ __used __visible void arch_rethook_tramp
#endif
regs->ip = (unsigned long)&arch_rethook_trampoline;
regs->orig_ax = ~0UL;
- regs->sp += sizeof(long);
- frame_pointer = ®s->sp + 1;
+ regs->sp += 2*sizeof(long);
+ frame_pointer = (long *)(regs + 1);
/*
* The return address at 'frame_pointer' is recovered by the
@@ -80,10 +82,10 @@ __used __visible void arch_rethook_tramp
rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
/*
- * Copy FLAGS to 'pt_regs::sp' so that arch_rethook_trapmoline()
+ * Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
* can do RET right after POPF.
*/
- regs->sp = regs->flags;
+ *(unsigned long *)®s->ss = regs->flags;
}
NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
@@ -101,7 +103,7 @@ STACK_FRAME_NON_STANDARD_FP(arch_rethook
void arch_rethook_fixup_return(struct pt_regs *regs,
unsigned long correct_ret_addr)
{
- unsigned long *frame_pointer = ®s->sp + 1;
+ unsigned long *frame_pointer = (void *)(regs + 1);
/* Replace fake return address with real one. */
*frame_pointer = correct_ret_addr;
next prev parent reply other threads:[~2022-03-25 11:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-25 4:28 [PATCH bpf-next 0/2] kprobes: rethook: x86: Replace kretprobe trampoline with rethook Masami Hiramatsu
2022-03-25 4:28 ` [PATCH bpf-next 1/2] kprobes: Use rethook for kretprobe if possible Masami Hiramatsu
2022-03-25 4:29 ` [PATCH bpf-next 2/2] rethook: kprobes: x86: Replace kretprobe with rethook on x86 Masami Hiramatsu
2022-03-25 10:09 ` Peter Zijlstra
2022-03-25 11:51 ` Jiri Olsa
2022-03-25 12:56 ` Masami Hiramatsu
2022-03-25 10:11 ` Peter Zijlstra
2022-03-25 11:40 ` Peter Zijlstra [this message]
2022-03-25 13:01 ` [PATCH bpf-next 3/2] x86,rethook: Fix arch_rethook_trampoline() to generate a complete pt_regs Masami Hiramatsu
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