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: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Chen Huang chenhuang5@huawei.com --- arch/arm64/lib/copy_from_user.S | 13 ++++++++++--- arch/arm64/lib/copy_in_user.S | 20 ++++++++++++++------ arch/arm64/lib/copy_to_user.S | 14 +++++++++++--- 3 files changed, 35 insertions(+), 12 deletions(-)
--- a/arch/arm64/lib/copy_from_user.S +++ b/arch/arm64/lib/copy_from_user.S @@ -39,7 +39,7 @@ .endm
.macro ldrh1 ptr, regB, val - uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val + uao_user_alternative 9997f, ldrh, ldtrh, \ptr, \regB, \val .endm
.macro strh1 ptr, regB, val @@ -47,7 +47,7 @@ .endm
.macro ldr1 ptr, regB, val - uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val + uao_user_alternative 9997f, ldr, ldtr, \ptr, \regB, \val .endm
.macro str1 ptr, regB, val @@ -55,7 +55,7 @@ .endm
.macro ldp1 ptr, regB, regC, val - uao_ldp 9998f, \ptr, \regB, \regC, \val + uao_ldp 9997f, \ptr, \regB, \regC, \val .endm
.macro stp1 ptr, regB, regC, val @@ -63,9 +63,11 @@ .endm
end .req x5 +srcin .req x15 ENTRY(__arch_copy_from_user) uaccess_enable_not_uao x3, x4, x5 add end, x0, x2 + mov srcin, x1 #include "copy_template.S" uaccess_disable_not_uao x3, x4 mov x0, #0 // Nothing to copy @@ -74,6 +76,11 @@ ENDPROC(__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 uaccess_disable_not_uao x3, x4 ret --- a/arch/arm64/lib/copy_in_user.S +++ b/arch/arm64/lib/copy_in_user.S @@ -40,34 +40,36 @@ .endm
.macro ldrh1 ptr, regB, val - uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val + uao_user_alternative 9997f, ldrh, ldtrh, \ptr, \regB, \val .endm
.macro strh1 ptr, regB, val - uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val + uao_user_alternative 9997f, strh, sttrh, \ptr, \regB, \val .endm
.macro ldr1 ptr, regB, val - uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val + uao_user_alternative 9997f, ldr, ldtr, \ptr, \regB, \val .endm
.macro str1 ptr, regB, val - uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val + uao_user_alternative 9997f, str, sttr, \ptr, \regB, \val .endm
.macro ldp1 ptr, regB, regC, val - uao_ldp 9998f, \ptr, \regB, \regC, \val + uao_ldp 9997f, \ptr, \regB, \regC, \val .endm
.macro stp1 ptr, regB, regC, val - uao_stp 9998f, \ptr, \regB, \regC, \val + uao_stp 9997f, \ptr, \regB, \regC, \val .endm
end .req x5 +srcin .req x15
ENTRY(__arch_copy_in_user) uaccess_enable_not_uao x3, x4, x5 add end, x0, x2 + mov srcin, x1 #include "copy_template.S" uaccess_disable_not_uao x3, x4 mov x0, #0 @@ -76,6 +78,12 @@ ENDPROC(__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 uaccess_disable_not_uao x3, x4 ret --- a/arch/arm64/lib/copy_to_user.S +++ b/arch/arm64/lib/copy_to_user.S @@ -42,7 +42,7 @@ .endm
.macro strh1 ptr, regB, val - uao_user_alternative 9998f, strh, sttrh, \ptr, \regB, \val + uao_user_alternative 9997f, strh, sttrh, \ptr, \regB, \val .endm
.macro ldr1 ptr, regB, val @@ -50,7 +50,7 @@ .endm
.macro str1 ptr, regB, val - uao_user_alternative 9998f, str, sttr, \ptr, \regB, \val + uao_user_alternative 9997f, str, sttr, \ptr, \regB, \val .endm
.macro ldp1 ptr, regB, regC, val @@ -58,13 +58,15 @@ .endm
.macro stp1 ptr, regB, regC, val - uao_stp 9998f, \ptr, \regB, \regC, \val + uao_stp 9997f, \ptr, \regB, \regC, \val .endm
end .req x5 +srcin .req x15 ENTRY(__arch_copy_to_user) uaccess_enable_not_uao x3, x4, x5 add end, x0, x2 + mov srcin, x1 #include "copy_template.S" uaccess_disable_not_uao x3, x4 mov x0, #0 @@ -73,6 +75,12 @@ ENDPROC(__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 uaccess_disable_not_uao x3, x4 ret