From dee87e09b0dd63da9b1e1876167ccae37842dfd0 Mon Sep 17 00:00:00 2001 From: Bijan Tabatabai Date: Thu, 16 Jul 2026 17:06:04 -0500 Subject: x86/pkeys: Fix pkey_alloc() return value when pkeys are not supported The man page for pkey_alloc(2) specifies that it should return -1 with the errno set to ENOSPC when pkeys are not supported [1]. However, on x86 pkey_alloc() sets errno to EINVAL when called for the first time on a CPU that does not support pkeys. The root cause of this is the x86 implementation of mm_pkey_alloc() not directly checking if pkeys are supported. It only checks if all the pkeys have been allocated by comparing the allocation map against all_pkeys_mask. When OSPKE is not enabled, init_new_context() skips the initialization of the allocation map, leaving it as 0, while all_pkeys_mask is 1. mm_pkey_alloc() interprets this as there being a pkey available and it returns pkey 0. Then, pkey_alloc() fails with -EINVAL from arch_set_user_pkey_access() instead of returning -ENOSPC. Subsequent calls to pkey_alloc() do return -ENOSPC because pkey 0 is left marked as allocated. Change mm_pkey_alloc() to directly check if OSPKE is enabled, and return -1 if it is not, which causes pkey_alloc() to return -ENOSPC. The arm64 and powerpc implementations of mm_pkey_alloc() already do this check. [1] https://man7.org/linux/man-pages/man2/pkey_alloc.2.html [ dhansen: use arch_pkeys_enabled() to follow arm ] Fixes: e8c24d3a23a4 ("x86/pkeys: Allocation/free syscalls") Signed-off-by: Bijan Tabatabai Signed-off-by: Dave Hansen Link: https://patch.msgid.link/20260716220604.26452-1-bijan311@gmail.com --- arch/x86/include/asm/pkeys.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h index 06ed2cd2592e..fcec52132fc7 100644 --- a/arch/x86/include/asm/pkeys.h +++ b/arch/x86/include/asm/pkeys.h @@ -88,6 +88,9 @@ int mm_pkey_alloc(struct mm_struct *mm) u16 all_pkeys_mask = ((1U << arch_max_pkey()) - 1); int ret; + if (!arch_pkeys_enabled()) + return -1; + /* * Are we out of pkeys? We must handle this specially * because ffz() behavior is undefined if there are no -- cgit v1.2.3