6.12-stable review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
commit 594bfc4947c4fcabba1318d8384c61a29a6b89fb upstream.
Currently poe_set() doesn't initialize the temporary 'ctrl' variable, and a SETREGSET call with a length of zero will leave this uninitialized. Consequently an arbitrary value will be written back to target->thread.por_el0, potentially leaking up to 64 bits of memory from the kernel stack. The read is limited to a specific slot on the stack, and the issue does not provide a write mechanism.
Fix this by initializing the temporary value before copying the regset from userspace, as for other regsets (e.g. NT_PRSTATUS, NT_PRFPREG, NT_ARM_SYSTEM_CALL). In the case of a zero-length write, the existing contents of POR_EL1 will be retained.
Before this patch:
| # ./poe-test | Attempting to write NT_ARM_POE::por_el0 = 0x900d900d900d900d | SETREGSET(nt=0x40f, len=8) wrote 8 bytes | | Attempting to read NT_ARM_POE::por_el0 | GETREGSET(nt=0x40f, len=8) read 8 bytes | Read NT_ARM_POE::por_el0 = 0x900d900d900d900d | | Attempting to write NT_ARM_POE (zero length) | SETREGSET(nt=0x40f, len=0) wrote 0 bytes | | Attempting to read NT_ARM_POE::por_el0 | GETREGSET(nt=0x40f, len=8) read 8 bytes | Read NT_ARM_POE::por_el0 = 0xffff8000839c3d50
After this patch:
| # ./poe-test | Attempting to write NT_ARM_POE::por_el0 = 0x900d900d900d900d | SETREGSET(nt=0x40f, len=8) wrote 8 bytes | | Attempting to read NT_ARM_POE::por_el0 | GETREGSET(nt=0x40f, len=8) read 8 bytes | Read NT_ARM_POE::por_el0 = 0x900d900d900d900d | | Attempting to write NT_ARM_POE (zero length) | SETREGSET(nt=0x40f, len=0) wrote 0 bytes | | Attempting to read NT_ARM_POE::por_el0 | GETREGSET(nt=0x40f, len=8) read 8 bytes | Read NT_ARM_POE::por_el0 = 0x900d900d900d900d
Fixes: 175198199262 ("arm64/ptrace: add support for FEAT_POE") Cc: stable@vger.kernel.org # 6.12.x Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Joey Gouly joey.gouly@arm.com Cc: Will Deacon will@kernel.org Reviewed-by: Mark Brown broonie@kernel.org Link: https://lore.kernel.org/r/20241205121655.1824269-4-mark.rutland@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/ptrace.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1469,6 +1469,8 @@ static int poe_set(struct task_struct *t if (!system_supports_poe()) return -EINVAL;
+ ctrl = target->thread.por_el0; + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &ctrl, 0, -1); if (ret) return ret;