From: Robin Murphy robin.murphy@arm.com

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.162609843... Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Chen Huang chenhuang5@huawei.com --- arch/arm64/lib/copy_from_user.S | 13 ++++++++++--- arch/arm64/lib/copy_in_user.S | 21 ++++++++++++++------- arch/arm64/lib/copy_to_user.S | 14 +++++++++++--- 3 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S index 0f8a3a9e3795..957a6d092d7a 100644 --- 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 80e37ada0ee1..35c01da09323 100644 --- 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 4ec59704b8f2..85705350ff35 100644 --- 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