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Message-Id: <20240927194925.069013308@infradead.org>
Date: Fri, 27 Sep 2024 21:49:03 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
peterz@...radead.org,
alyssa.milburn@...el.com,
scott.d.constable@...el.com,
joao@...rdrivepizza.com,
andrew.cooper3@...rix.com,
jpoimboe@...nel.org,
jose.marchesi@...cle.com,
hjl.tools@...il.com,
ndesaulniers@...gle.com,
samitolvanen@...gle.com,
nathan@...nel.org,
ojeda@...nel.org,
kees@...nel.org,
alexei.starovoitov@...il.com,
Andrii Nakryiko <andrii@...nel.org>
Subject: [PATCH 07/14] x86/ibt: Clean up is_endbr()
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.
Note: this effectively reverts commit a8497506cd2c ("bpf: Avoid
get_kernel_nofault() to fetch kprobe entry IP") which was entirely the
wrong way to go about doing things. The right solution is to optimize
get_kernel_nofault() itself, it really doesn't need STAC/CLAC nor the
speculation barrier. Using __get_user is a historical hack, not a
requirement.
Cc: Andrii Nakryiko <andrii@...nel.org>
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 | 19 +++++++++++++------
arch/x86/kernel/kprobes/core.c | 11 +----------
arch/x86/net/bpf_jit_comp.c | 4 ++--
kernel/trace/bpf_trace.c | 14 ++------------
6 files changed, 22 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 +852,23 @@ void __init_or_module noinline apply_ret
#ifdef CONFIG_X86_KERNEL_IBT
+__noendbr bool is_endbr(u32 *val)
+{
+ u32 endbr;
+
+ if (get_kernel_nofault(endbr, val))
+ return false;
+
+ return __is_endbr(endbr);
+}
+
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 +995,7 @@ 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
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