arm64: Avoid premature usercopy failure

commit 295cf156231ca3f9e3a66bde7fab5e09c41835e0 upstream.

Al reminds us that the usercopy API must only return complete failure
if absolutely nothing could be copied. Currently, if userspace does
something silly like giving us an unaligned pointer to Device memory,
or a size which overruns MTE tag bounds, we may fail to honour that
requirement when faulting on a multi-byte access even though a smaller
access could have succeeded.

Add a mitigation to the fixup routines to fall back to a single-byte
copy if we faulted on a larger access before anything has been written
to the destination, to guarantee making *some* forward progress. We
needn't be too concerned about the overall performance since this should
only occur when callers are doing something a bit dodgy in the first
place. Particularly broken userspace might still be able to trick
generic_perform_write() into an infinite loop by targeting write() at
an mmap() of some read-only device register where the fault-in load
succeeds but any store synchronously aborts such that copy_to_user() is
genuinely unable to make progress, but, well, don't do that...

CC: stable@vger.kernel.org
Reported-by: Chen Huang <chenhuang5@huawei.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/dc03d5c675731a1f24a62417dba5429ad744234e.1626098433.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Chen Huang <chenhuang5@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 0f8a3a9e3795b64b6cb0e53c0953e3b1833884e4..957a6d092d7af83771ea09395f73d87f1015235e 100644 (file)
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -29,7 +29,7 @@
        .endm
 
        .macro ldrh1 reg, ptr, val
-       uao_user_alternative 9998f, ldrh, ldtrh, \reg, \ptr, \val
+       uao_user_alternative 9997f, ldrh, ldtrh, \reg, \ptr, \val
        .endm
 
        .macro strh1 reg, ptr, val
@@ -37,7 +37,7 @@
        .endm
 
        .macro ldr1 reg, ptr, val
-       uao_user_alternative 9998f, ldr, ldtr, \reg, \ptr, \val
+       uao_user_alternative 9997f, ldr, ldtr, \reg, \ptr, \val
        .endm
 
        .macro str1 reg, ptr, val
@@ -45,7 +45,7 @@
        .endm
 
        .macro ldp1 reg1, reg2, ptr, val
-       uao_ldp 9998f, \reg1, \reg2, \ptr, \val
+       uao_ldp 9997f, \reg1, \reg2, \ptr, \val
        .endm
 
        .macro stp1 reg1, reg2, ptr, val
@@ -53,8 +53,10 @@
        .endm
 
 end    .req    x5
+srcin  .req    x15
 SYM_FUNC_START(__arch_copy_from_user)
        add     end, x0, x2
+       mov     srcin, x1
 #include "copy_template.S"
        mov     x0, #0                          // Nothing to copy
        ret
@@ -63,6 +65,11 @@ EXPORT_SYMBOL(__arch_copy_from_user)
 
        .section .fixup,"ax"
        .align  2
+9997:  cmp     dst, dstin
+       b.ne    9998f
+       // Before being absolutely sure we couldn't copy anything, try harder
+USER(9998f, ldtrb tmp1w, [srcin])
+       strb    tmp1w, [dst], #1
 9998:  sub     x0, end, dst                    // bytes not copied
        ret
        .previous

diff --git a/arch/arm64/lib/copy_in_user.S b/arch/arm64/lib/copy_in_user.S
index 80e37ada0ee1a501d5d4fb9fe87db9fc5853af2b..35c01da09323ee6de85494efed8e760fbe453206 100644 (file)
--- a/arch/arm64/lib/copy_in_user.S
+++ b/arch/arm64/lib/copy_in_user.S
@@ -30,33 +30,34 @@
        .endm
 
        .macro ldrh1 reg, ptr, val
-       uao_user_alternative 9998f, ldrh, ldtrh, \reg, \ptr, \val
+       uao_user_alternative 9997f, ldrh, ldtrh, \reg, \ptr, \val
        .endm
 
        .macro strh1 reg, ptr, val
-       uao_user_alternative 9998f, strh, sttrh, \reg, \ptr, \val
+       uao_user_alternative 9997f, strh, sttrh, \reg, \ptr, \val
        .endm
 
        .macro ldr1 reg, ptr, val
-       uao_user_alternative 9998f, ldr, ldtr, \reg, \ptr, \val
+       uao_user_alternative 9997f, ldr, ldtr, \reg, \ptr, \val
        .endm
 
        .macro str1 reg, ptr, val
-       uao_user_alternative 9998f, str, sttr, \reg, \ptr, \val
+       uao_user_alternative 9997f, str, sttr, \reg, \ptr, \val
        .endm
 
        .macro ldp1 reg1, reg2, ptr, val
-       uao_ldp 9998f, \reg1, \reg2, \ptr, \val
+       uao_ldp 9997f, \reg1, \reg2, \ptr, \val
        .endm
 
        .macro stp1 reg1, reg2, ptr, val
-       uao_stp 9998f, \reg1, \reg2, \ptr, \val
+       uao_stp 9997f, \reg1, \reg2, \ptr, \val
        .endm
 
 end    .req    x5
-
+srcin  .req    x15
 SYM_FUNC_START(__arch_copy_in_user)
        add     end, x0, x2
+       mov     srcin, x1
 #include "copy_template.S"
        mov     x0, #0
        ret
@@ -65,6 +66,12 @@ EXPORT_SYMBOL(__arch_copy_in_user)
 
        .section .fixup,"ax"
        .align  2
+9997:  cmp     dst, dstin
+       b.ne    9998f
+       // Before being absolutely sure we couldn't copy anything, try harder
+USER(9998f, ldtrb tmp1w, [srcin])
+USER(9998f, sttrb tmp1w, [dst])
+       add     dst, dst, #1
 9998:  sub     x0, end, dst                    // bytes not copied
        ret
        .previous

diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 4ec59704b8f2d19933ec1f39ca48e76315309609..85705350ff35457c03320bce3192a626732cd16a 100644 (file)
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -32,7 +32,7 @@
        .endm
 
        .macro strh1 reg, ptr, val
-       uao_user_alternative 9998f, strh, sttrh, \reg, \ptr, \val
+       uao_user_alternative 9997f, strh, sttrh, \reg, \ptr, \val
        .endm
 
        .macro ldr1 reg, ptr, val
@@ -40,7 +40,7 @@
        .endm
 
        .macro str1 reg, ptr, val
-       uao_user_alternative 9998f, str, sttr, \reg, \ptr, \val
+       uao_user_alternative 9997f, str, sttr, \reg, \ptr, \val
        .endm
 
        .macro ldp1 reg1, reg2, ptr, val
@@ -48,12 +48,14 @@
        .endm
 
        .macro stp1 reg1, reg2, ptr, val
-       uao_stp 9998f, \reg1, \reg2, \ptr, \val
+       uao_stp 9997f, \reg1, \reg2, \ptr, \val
        .endm
 
 end    .req    x5
+srcin  .req    x15
 SYM_FUNC_START(__arch_copy_to_user)
        add     end, x0, x2
+       mov     srcin, x1
 #include "copy_template.S"
        mov     x0, #0
        ret
@@ -62,6 +64,12 @@ EXPORT_SYMBOL(__arch_copy_to_user)
 
        .section .fixup,"ax"
        .align  2
+9997:  cmp     dst, dstin
+       b.ne    9998f
+       // Before being absolutely sure we couldn't copy anything, try harder
+       ldrb    tmp1w, [srcin]
+USER(9998f, sttrb tmp1w, [dst])
+       add     dst, dst, #1
 9998:  sub     x0, end, dst                    // bytes not copied
        ret
        .previous