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uprobes/x86: Accept more NOP forms

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Instead of only accepting the x86_64 nop5 chosen by the kernel, accept
any x86_64 NOP or NOPL instruction that is 5 bytes.

Notably, the x86_64 nop5 pattern is valid in 32bit apps and could get
compiler generated when build for i686 (which introduced NOPL). Since
the trampoline is x86_64 only, make sure to limit to x86_64 code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250821123656.935559566@infradead.org
This commit is contained in:
Peter Zijlstra 2025-08-20 12:55:14 +02:00
parent fd54052b60
commit 7c2bfc183b
1 changed files with 32 additions and 5 deletions
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37
arch/x86/kernel/uprobes.c
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@ -1157,10 +1157,37 @@ void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
mmap_write_unlock(mm);
}
static bool can_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
static bool insn_is_nop(struct insn *insn)
{
if (memcmp(&auprobe->insn, x86_nops[5], 5))
return insn->opcode.nbytes == 1 && insn->opcode.bytes[0] == 0x90;
}
static bool insn_is_nopl(struct insn *insn)
{
if (insn->opcode.nbytes != 2)
return false;
if (insn->opcode.bytes[0] != 0x0f || insn->opcode.bytes[1] != 0x1f)
return false;
if (!insn->modrm.nbytes)
return false;
if (X86_MODRM_REG(insn->modrm.bytes[0]) != 0)
return false;
/* 0f 1f /0 - NOPL */
return true;
}
static bool can_optimize(struct insn *insn, unsigned long vaddr)
{
if (!insn->x86_64 || insn->length != 5)
return false;
if (!insn_is_nop(insn) && !insn_is_nopl(insn))
return false;
/* We can't do cross page atomic writes yet. */
return PAGE_SIZE - (vaddr & ~PAGE_MASK) >= 5;
}
@ -1177,7 +1204,7 @@ static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
}
static bool can_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
static bool can_optimize(struct insn *insn, unsigned long vaddr)
{
return false;
}
@ -1539,15 +1566,15 @@ static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
*/
int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long addr)
{
struct insn insn;
u8 fix_ip_or_call = UPROBE_FIX_IP;
struct insn insn;
int ret;
ret = uprobe_init_insn(auprobe, &insn, is_64bit_mm(mm));
if (ret)
return ret;
if (can_optimize(auprobe, addr))
if (can_optimize(&insn, addr))
set_bit(ARCH_UPROBE_FLAG_CAN_OPTIMIZE, &auprobe->flags);
ret = branch_setup_xol_ops(auprobe, &insn);