[PATCH v2] x86: Allow user accesses to the base of the guard page

[David Laight <David.Laight@ACULAB.COM>]

__access_ok() calls valid_user_address() with the address after
the last byte of the user buffer.
It is valid for a buffer to end with the last valid user address
so valid_user_address() must allow accesses to the base of the
guard page.

Fixes: 86e6b1547b3d0 ("x86: fix user address masking non-canonical speculation issue")
Signed-off-by: David Laight <david.laight@aculab.com>
---

v2: Rewritten commit message.

 arch/x86/kernel/cpu/common.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 06a516f6795b..ca327cfa42ae 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2389,12 +2389,12 @@ void __init arch_cpu_finalize_init(void)
 	alternative_instructions();
 
 	if (IS_ENABLED(CONFIG_X86_64)) {
-		unsigned long USER_PTR_MAX = TASK_SIZE_MAX-1;
+		unsigned long USER_PTR_MAX = TASK_SIZE_MAX;
 
 		/*
 		 * Enable this when LAM is gated on LASS support
 		if (cpu_feature_enabled(X86_FEATURE_LAM))
-			USER_PTR_MAX = (1ul << 63) - PAGE_SIZE - 1;
+			USER_PTR_MAX = (1ul << 63) - PAGE_SIZE;
 		 */
 		runtime_const_init(ptr, USER_PTR_MAX);
 
-- 
2.17.1

-
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