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ARM: 9481/2: breakpoint: CFI breakpoints only on demand

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This removes the stub hw_breakpoint_cfi_handler() from ARM, making
it not steal breakpoint type 0x03 (ARM_ENTRY_CFI_BREAKPOINT) unless
CFI is actively used in the kernel.

When not instrumenting with CFI, or when a breakpoint is issued in
userspace, we fall through to return 1 from hw_breakpoint_pending()
"unhandled fault" so userspace can make use of this breakpoint.

Tested with LKDTM and this command line:
echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT
still works as expected.

Closes: https://lore.kernel.org/lkml/kJqktbpLphg_Pk5I5SPptgTLjl3E3eq5mN5UzCslyFj7Q1Irp-wDid4mj5eQVd2iZtRGXgeZd8goq195EkXdjyt864YMc8mVb2B9NGH91NQ=@protonmail.com/

Fixes: c3f89986fd ("ARM: 9391/2: hw_breakpoint: Handle CFI breakpoints")
Reported-by: slipher <slipher@protonmail.com>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Linus Walleij 2026-07-04 21:15:55 +01:00 committed by Russell King
parent 7e8ee82e69
commit 8ed9bff906
1 changed files with 6 additions and 5 deletions
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11
arch/arm/kernel/hw_breakpoint.c
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@ -929,10 +929,6 @@ static void hw_breakpoint_cfi_handler(struct pt_regs *regs)
break;
}
}
#else
static void hw_breakpoint_cfi_handler(struct pt_regs *regs)
{
}
#endif
/*
@ -964,9 +960,14 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
case ARM_ENTRY_SYNC_WATCHPOINT:
watchpoint_handler(addr, fsr, regs);
break;
#ifdef CONFIG_CFI
case ARM_ENTRY_CFI_BREAKPOINT:
hw_breakpoint_cfi_handler(regs);
if (user_mode(regs))
ret = 1; /* Don't handle userspace BKPT */
else
hw_breakpoint_cfi_handler(regs);
break;
#endif
default:
ret = 1; /* Unhandled fault. */
}