| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20240930093302.GB33184@noisy.programming.kicks-ass.net>
Date: Mon, 30 Sep 2024 11:33:02 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
alyssa.milburn@...el.com, scott.d.constable@...el.com,
Joao Moreira <joao@...rdrivepizza.com>,
Andrew Cooper <andrew.cooper3@...rix.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
"Jose E. Marchesi" <jose.marchesi@...cle.com>,
"H.J. Lu" <hjl.tools@...il.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Nathan Chancellor <nathan@...nel.org>, ojeda@...nel.org,
Kees Cook <kees@...nel.org>
Subject: Re: [PATCH 07/14] x86/ibt: Clean up is_endbr()
On Mon, Sep 30, 2024 at 10:30:26AM +0200, Peter Zijlstra wrote:
> On Sun, Sep 29, 2024 at 10:32:38AM -0700, Alexei Starovoitov wrote:
> > On Fri, Sep 27, 2024 at 12:50 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -1027,19 +1027,9 @@ static const struct bpf_func_proto bpf_g
> > > #ifdef CONFIG_X86_KERNEL_IBT
> > > static unsigned long get_entry_ip(unsigned long fentry_ip)
> > > {
> > > - u32 instr;
> > > + if (is_endbr((void *)(fentry_ip - ENDBR_INSN_SIZE)))
> > > + return fentry_ip - ENDBR_INSN_SIZE;
> > >
> > > - /* We want to be extra safe in case entry ip is on the page edge,
> > > - * but otherwise we need to avoid get_kernel_nofault()'s overhead.
> > > - */
> > > - if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
> > > - if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
> > > - return fentry_ip;
> > > - } else {
> > > - instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
> > > - }
> > > - if (is_endbr(instr))
> > > - fentry_ip -= ENDBR_INSN_SIZE;
> > > return fentry_ip;
> >
> > Pls don't.
> >
> > This re-introduces the overhead that we want to avoid.
> >
> > Just call __is_endbr() here and keep the optimization.
>
> Well, I could do that ofcourse, but as I wrote elsewhere, the right
> thing to do is to optimize get_kernel_nofault(), its current
> implementation is needlessly expensive. All we really need is a load
> with an exception entry, the STAC/CLAC and speculation nonsense should
> not be needed.
Looking at things, something like the below actually generates sane
code:
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a582cd25ca87..84f65ee9736c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1029,17 +1029,10 @@ static unsigned long get_entry_ip(unsigned long fentry_ip)
{
u32 instr;
- /* We want to be extra safe in case entry ip is on the page edge,
- * but otherwise we need to avoid get_kernel_nofault()'s overhead.
- */
- if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
- if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
- return fentry_ip;
- } else {
- instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
- }
+ __get_kernel_nofault(&instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE), u32, Efault);
if (is_endbr(instr))
fentry_ip -= ENDBR_INSN_SIZE;
+Efault:
return fentry_ip;
}
#else
Which then leads to me rewriting the proposed patch as...
---
Subject: x86/ibt: Clean up is_endbr()
From: Peter Zijlstra <peterz@...radead.org>
Pretty much every caller of is_endbr() actually wants to test something at an
address and ends up doing get_kernel_nofault(). Fold the lot into a more
convenient helper.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/events/core.c | 2 +-
arch/x86/include/asm/ibt.h | 5 +++--
arch/x86/kernel/alternative.c | 20 ++++++++++++++------
arch/x86/kernel/kprobes/core.c | 11 +----------
arch/x86/net/bpf_jit_comp.c | 4 ++--
kernel/trace/bpf_trace.c | 14 ++------------
6 files changed, 23 insertions(+), 33 deletions(-)
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2845,7 +2845,7 @@ static bool is_uprobe_at_func_entry(stru
return true;
/* endbr64 (64-bit only) */
- if (user_64bit_mode(regs) && is_endbr(*(u32 *)auprobe->insn))
+ if (user_64bit_mode(regs) && is_endbr((u32 *)auprobe->insn))
return true;
return false;
--- a/arch/x86/include/asm/ibt.h
+++ b/arch/x86/include/asm/ibt.h
@@ -65,7 +65,7 @@ static __always_inline __attribute_const
return 0x001f0f66; /* osp nopl (%rax) */
}
-static inline bool is_endbr(u32 val)
+static inline bool __is_endbr(u32 val)
{
if (val == gen_endbr_poison())
return true;
@@ -74,6 +74,7 @@ static inline bool is_endbr(u32 val)
return val == gen_endbr();
}
+extern __noendbr bool is_endbr(u32 *val);
extern __noendbr u64 ibt_save(bool disable);
extern __noendbr void ibt_restore(u64 save);
@@ -102,7 +103,7 @@ extern bool __do_kernel_cp_fault(struct
#define __noendbr
-static inline bool is_endbr(u32 val) { return false; }
+static inline bool is_endbr(u32 *val) { return false; }
static inline u64 ibt_save(bool disable) { return 0; }
static inline void ibt_restore(u64 save) { }
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -852,16 +852,24 @@ void __init_or_module noinline apply_ret
#ifdef CONFIG_X86_KERNEL_IBT
+__noendbr bool is_endbr(u32 *val)
+{
+ u32 endbr;
+
+ __get_kernel_nofault(&endbr, val, u32, Efault);
+ return __is_endbr(endbr);
+
+Efault:
+ return false;
+}
+
static void poison_cfi(void *addr);
static void __init_or_module poison_endbr(void *addr, bool warn)
{
- u32 endbr, poison = gen_endbr_poison();
-
- if (WARN_ON_ONCE(get_kernel_nofault(endbr, addr)))
- return;
+ u32 poison = gen_endbr_poison();
- if (!is_endbr(endbr)) {
+ if (!is_endbr(addr)) {
WARN_ON_ONCE(warn);
return;
}
@@ -988,7 +996,7 @@ static u32 cfi_seed __ro_after_init;
static u32 cfi_rehash(u32 hash)
{
hash ^= cfi_seed;
- while (unlikely(is_endbr(hash) || is_endbr(-hash))) {
+ while (unlikely(__is_endbr(hash) || __is_endbr(-hash))) {
bool lsb = hash & 1;
hash >>= 1;
if (lsb)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -373,16 +373,7 @@ static bool can_probe(unsigned long padd
kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
bool *on_func_entry)
{
- u32 insn;
-
- /*
- * Since 'addr' is not guaranteed to be safe to access, use
- * copy_from_kernel_nofault() to read the instruction:
- */
- if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(u32)))
- return NULL;
-
- if (is_endbr(insn)) {
+ if (is_endbr((u32 *)addr)) {
*on_func_entry = !offset || offset == 4;
if (*on_func_entry)
offset = 4;
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -625,7 +625,7 @@ int bpf_arch_text_poke(void *ip, enum bp
* See emit_prologue(), for IBT builds the trampoline hook is preceded
* with an ENDBR instruction.
*/
- if (is_endbr(*(u32 *)ip))
+ if (is_endbr(ip))
ip += ENDBR_INSN_SIZE;
return __bpf_arch_text_poke(ip, t, old_addr, new_addr);
@@ -2971,7 +2971,7 @@ static int __arch_prepare_bpf_trampoline
/* skip patched call instruction and point orig_call to actual
* body of the kernel function.
*/
- if (is_endbr(*(u32 *)orig_call))
+ if (is_endbr(orig_call))
orig_call += ENDBR_INSN_SIZE;
orig_call += X86_PATCH_SIZE;
}
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1027,19 +1027,9 @@ static const struct bpf_func_proto bpf_g
#ifdef CONFIG_X86_KERNEL_IBT
static unsigned long get_entry_ip(unsigned long fentry_ip)
{
- u32 instr;
+ if (is_endbr((void *)(fentry_ip - ENDBR_INSN_SIZE)))
+ return fentry_ip - ENDBR_INSN_SIZE;
- /* We want to be extra safe in case entry ip is on the page edge,
- * but otherwise we need to avoid get_kernel_nofault()'s overhead.
- */
- if ((fentry_ip & ~PAGE_MASK) < ENDBR_INSN_SIZE) {
- if (get_kernel_nofault(instr, (u32 *)(fentry_ip - ENDBR_INSN_SIZE)))
- return fentry_ip;
- } else {
- instr = *(u32 *)(fentry_ip - ENDBR_INSN_SIZE);
- }
- if (is_endbr(instr))
- fentry_ip -= ENDBR_INSN_SIZE;
return fentry_ip;
}
#else
Powered by blists - more mailing lists