[PATCH 08/10] x86: remove address space overrides using set_fs()

From: Christoph Hellwig
Date: Thu Aug 27 2020 - 11:04:42 EST

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Stop providing the possibility to override the address space using
set_fs() now that there is no need for that any more. To properly
handle the TASK_SIZE_MAX checking for 4 vs 5-level page tables on
x86 a new alternative is introduced, which just like the one in
entry_64.S has to use the hardcoded virtual address bits to escape
the fact that TASK_SIZE_MAX isn't actually a constant when 5-level
page tables are enabled.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/x86/Kconfig | 1 -
arch/x86/ia32/ia32_aout.c | 1 -
arch/x86/include/asm/processor.h | 11 +----------
arch/x86/include/asm/thread_info.h | 2 --
arch/x86/include/asm/uaccess.h | 26 +-------------------------
arch/x86/kernel/asm-offsets.c | 3 ---
arch/x86/lib/getuser.S | 28 ++++++++++++++++++----------
arch/x86/lib/putuser.S | 21 ++++++++++++---------
8 files changed, 32 insertions(+), 61 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f85c13355732fe..7101ac64bb209d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -237,7 +237,6 @@ config X86
select HAVE_ARCH_KCSAN if X86_64
select X86_FEATURE_NAMES if PROC_FS
select PROC_PID_ARCH_STATUS if PROC_FS
- select SET_FS
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI

config INSTRUCTION_DECODER
diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index ca8a657edf5977..a09fc37ead9d47 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -239,7 +239,6 @@ static int load_aout_binary(struct linux_binprm *bprm)
(regs)->ss = __USER32_DS;
regs->r8 = regs->r9 = regs->r10 = regs->r11 =
regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;
- set_fs(USER_DS);
return 0;
}

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 1618eeb08361a9..189573d95c3af6 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -482,10 +482,6 @@ extern unsigned int fpu_user_xstate_size;

struct perf_event;

-typedef struct {
- unsigned long seg;
-} mm_segment_t;
-
struct thread_struct {
/* Cached TLS descriptors: */
struct desc_struct tls_array[GDT_ENTRY_TLS_ENTRIES];
@@ -538,8 +534,6 @@ struct thread_struct {
*/
unsigned long iopl_emul;

- mm_segment_t addr_limit;
-
unsigned int sig_on_uaccess_err:1;

/* Floating point and extended processor state */
@@ -785,15 +779,12 @@ static inline void spin_lock_prefetch(const void *x)
#define INIT_THREAD { \
.sp0 = TOP_OF_INIT_STACK, \
.sysenter_cs = __KERNEL_CS, \
- .addr_limit = KERNEL_DS, \
}

#define KSTK_ESP(task) (task_pt_regs(task)->sp)

#else
-#define INIT_THREAD { \
- .addr_limit = KERNEL_DS, \
-}
+#define INIT_THREAD { }

extern unsigned long KSTK_ESP(struct task_struct *task);

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 267701ae3d86dd..44733a4bfc4294 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -102,7 +102,6 @@ struct thread_info {
#define TIF_SYSCALL_TRACEPOINT 28 /* syscall tracepoint instrumentation */
#define TIF_ADDR32 29 /* 32-bit address space on 64 bits */
#define TIF_X32 30 /* 32-bit native x86-64 binary */
-#define TIF_FSCHECK 31 /* Check FS is USER_DS on return */

#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
@@ -131,7 +130,6 @@ struct thread_info {
#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
#define _TIF_ADDR32 (1 << TIF_ADDR32)
#define _TIF_X32 (1 << TIF_X32)
-#define _TIF_FSCHECK (1 << TIF_FSCHECK)

/* flags to check in __switch_to() */
#define _TIF_WORK_CTXSW_BASE \
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index ecefaffd15d4c8..a4ceda0510ea87 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -12,30 +12,6 @@
#include <asm/smap.h>
#include <asm/extable.h>

-/*
- * The fs value determines whether argument validity checking should be
- * performed or not. If get_fs() == USER_DS, checking is performed, with
- * get_fs() == KERNEL_DS, checking is bypassed.
- *
- * For historical reasons, these macros are grossly misnamed.
- */
-
-#define MAKE_MM_SEG(s) ((mm_segment_t) { (s) })
-
-#define KERNEL_DS MAKE_MM_SEG(-1UL)
-#define USER_DS MAKE_MM_SEG(TASK_SIZE_MAX)
-
-#define get_fs() (current->thread.addr_limit)
-static inline void set_fs(mm_segment_t fs)
-{
- current->thread.addr_limit = fs;
- /* On user-mode return, check fs is correct */
- set_thread_flag(TIF_FSCHECK);
-}
-
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-#define user_addr_max() (current->thread.addr_limit.seg)
-
/*
* Test whether a block of memory is a valid user space address.
* Returns 0 if the range is valid, nonzero otherwise.
@@ -93,7 +69,7 @@ static inline bool pagefault_disabled(void);
#define access_ok(addr, size) \
({ \
WARN_ON_IN_IRQ(); \
- likely(!__range_not_ok(addr, size, user_addr_max())); \
+ likely(!__range_not_ok(addr, size, TASK_SIZE_MAX)); \
})

/*
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 3ca07ad552ae0c..70b7154f4bdd62 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -37,9 +37,6 @@ static void __used common(void)
OFFSET(TASK_stack_canary, task_struct, stack_canary);
#endif

- BLANK();
- OFFSET(TASK_addr_limit, task_struct, thread.addr_limit);
-
BLANK();
OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);

diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index c8a85b512796e1..ccc9808c66420a 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -35,10 +35,18 @@
#include <asm/smap.h>
#include <asm/export.h>

+#ifdef CONFIG_X86_5LEVEL
+#define LOAD_TASK_SIZE_MAX \
+ ALTERNATIVE "mov $((1 << 47) - 4096),%rdx", \
+ "mov $((1 << 56) - 4096),%rdx", X86_FEATURE_LA57
+#else
+#define LOAD_TASK_SIZE_MAX mov $TASK_SIZE_MAX,%_ASM_DX
+#endif
+
.text
SYM_FUNC_START(__get_user_1)
- mov PER_CPU_VAR(current_task), %_ASM_DX
- cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_DX,%_ASM_AX
jae bad_get_user
sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
and %_ASM_DX, %_ASM_AX
@@ -53,8 +61,8 @@ EXPORT_SYMBOL(__get_user_1)
SYM_FUNC_START(__get_user_2)
add $1,%_ASM_AX
jc bad_get_user
- mov PER_CPU_VAR(current_task), %_ASM_DX
- cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_DX,%_ASM_AX
jae bad_get_user
sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
and %_ASM_DX, %_ASM_AX
@@ -69,8 +77,8 @@ EXPORT_SYMBOL(__get_user_2)
SYM_FUNC_START(__get_user_4)
add $3,%_ASM_AX
jc bad_get_user
- mov PER_CPU_VAR(current_task), %_ASM_DX
- cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_DX,%_ASM_AX
jae bad_get_user
sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
and %_ASM_DX, %_ASM_AX
@@ -86,8 +94,8 @@ SYM_FUNC_START(__get_user_8)
#ifdef CONFIG_X86_64
add $7,%_ASM_AX
jc bad_get_user
- mov PER_CPU_VAR(current_task), %_ASM_DX
- cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_DX,%_ASM_AX
jae bad_get_user
sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
and %_ASM_DX, %_ASM_AX
@@ -99,8 +107,8 @@ SYM_FUNC_START(__get_user_8)
#else
add $7,%_ASM_AX
jc bad_get_user_8
- mov PER_CPU_VAR(current_task), %_ASM_DX
- cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_DX,%_ASM_AX
jae bad_get_user_8
sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
and %_ASM_DX, %_ASM_AX
diff --git a/arch/x86/lib/putuser.S b/arch/x86/lib/putuser.S
index 7c7c92db8497af..f5a56394985875 100644
--- a/arch/x86/lib/putuser.S
+++ b/arch/x86/lib/putuser.S
@@ -31,12 +31,18 @@
* as they get called from within inline assembly.
*/

-#define ENTER mov PER_CPU_VAR(current_task), %_ASM_BX
+#ifdef CONFIG_X86_5LEVEL
+#define LOAD_TASK_SIZE_MAX \
+ ALTERNATIVE "mov $((1 << 47) - 4096),%rbx", \
+ "mov $((1 << 56) - 4096),%rbx", X86_FEATURE_LA57
+#else
+#define LOAD_TASK_SIZE_MAX mov $TASK_SIZE_MAX,%_ASM_BX
+#endif

.text
SYM_FUNC_START(__put_user_1)
- ENTER
- cmp TASK_addr_limit(%_ASM_BX),%_ASM_CX
+ LOAD_TASK_SIZE_MAX
+ cmp %_ASM_BX,%_ASM_CX
jae .Lbad_put_user
ASM_STAC
1: movb %al,(%_ASM_CX)
@@ -47,8 +53,7 @@ SYM_FUNC_END(__put_user_1)
EXPORT_SYMBOL(__put_user_1)

SYM_FUNC_START(__put_user_2)
- ENTER
- mov TASK_addr_limit(%_ASM_BX),%_ASM_BX
+ LOAD_TASK_SIZE_MAX
sub $1,%_ASM_BX
cmp %_ASM_BX,%_ASM_CX
jae .Lbad_put_user
@@ -61,8 +66,7 @@ SYM_FUNC_END(__put_user_2)
EXPORT_SYMBOL(__put_user_2)

SYM_FUNC_START(__put_user_4)
- ENTER
- mov TASK_addr_limit(%_ASM_BX),%_ASM_BX
+ LOAD_TASK_SIZE_MAX
sub $3,%_ASM_BX
cmp %_ASM_BX,%_ASM_CX
jae .Lbad_put_user
@@ -75,8 +79,7 @@ SYM_FUNC_END(__put_user_4)
EXPORT_SYMBOL(__put_user_4)

SYM_FUNC_START(__put_user_8)
- ENTER
- mov TASK_addr_limit(%_ASM_BX),%_ASM_BX
+ LOAD_TASK_SIZE_MAX
sub $7,%_ASM_BX
cmp %_ASM_BX,%_ASM_CX
jae .Lbad_put_user
--
2.28.0

Next message: Keith Busch: "Re: [PATCH] nvme-pci: cancel nvme device request before disabling"
Previous message: Christoph Hellwig: "[PATCH 07/10] x86: make TASK_SIZE_MAX usable from assembly code"
In reply to: Christoph Hellwig: "[PATCH 07/10] x86: make TASK_SIZE_MAX usable from assembly code"
Next in thread: Linus Torvalds: "Re: [PATCH 08/10] x86: remove address space overrides using set_fs()"
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