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ARM: uaccess: add further explanation of __range_ok()

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Detail the success return condition, and that we rely on KERNEL_DS
being zero for this to operate correctly.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Russell King
2020-07-22 09:50:23 +01:00
parent 6da5238fa3
commit 2350ebe2c4
1 changed files with 5 additions and 1 deletions
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6
arch/arm/include/asm/uaccess.h
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@@ -78,7 +78,11 @@ static inline void set_fs(mm_segment_t fs)
#define segment_eq(a, b) ((a) == (b)) #define segment_eq(a, b) ((a) == (b))
/* We use 33-bit arithmetic here... */ /*
* We use 33-bit arithmetic here. Success returns zero, failure returns
* addr_limit. We take advantage that addr_limit will be zero for KERNEL_DS,
* so this will always return success in that case.
*/
#define __range_ok(addr, size) ({ \ #define __range_ok(addr, size) ({ \
unsigned long flag, roksum; \ unsigned long flag, roksum; \
__chk_user_ptr(addr); \ __chk_user_ptr(addr); \