| Message ID | dc03d5c675731a1f24a62417dba5429ad744234e.1626098433.git.robin.murphy@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: Avoid premature usercopy failure | expand |
On Mon, Jul 12, 2021 at 03:27:46PM +0100, Robin Murphy wrote: > 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> > --- > > I've started trying the "replay" approach for figuring out more precise > remainders in general, but that quickly got more complicated with > rebasing the fault address passing stuff, so I'm resending this now as > a point fix and will continue to explore that as an improvement on top. Is it possible to add/extend a selftest for this, please? I think Catalin mentioned that before, but not sure if he got anywhere with it. Will
On Tue, Jul 13, 2021 at 05:59:58PM +0100, Will Deacon wrote: > On Mon, Jul 12, 2021 at 03:27:46PM +0100, Robin Murphy wrote: > > 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> > > --- > > > > I've started trying the "replay" approach for figuring out more precise > > remainders in general, but that quickly got more complicated with > > rebasing the fault address passing stuff, so I'm resending this now as > > a point fix and will continue to explore that as an improvement on top. > > Is it possible to add/extend a selftest for this, please? I think Catalin > mentioned that before, but not sure if he got anywhere with it. It's on my to-do list but going on holiday soon. If Robin is keen on this, I don't really mind ;).
On Mon, 12 Jul 2021 15:27:46 +0100, Robin Murphy wrote: > 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. > > [...] Applied to arm64 (for-next/fixes), thanks! [1/1] arm64: Avoid premature usercopy failure https://git.kernel.org/arm64/c/295cf156231c Cheers,
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S index 95cd62d67371..2cf999e41d30 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 - user_ldst 9998f, ldtrh, \reg, \ptr, \val + user_ldst 9997f, ldtrh, \reg, \ptr, \val .endm .macro strh1 reg, ptr, val @@ -37,7 +37,7 @@ .endm .macro ldr1 reg, ptr, val - user_ldst 9998f, ldtr, \reg, \ptr, \val + user_ldst 9997f, ldtr, \reg, \ptr, \val .endm .macro str1 reg, ptr, val @@ -45,7 +45,7 @@ .endm .macro ldp1 reg1, reg2, ptr, val - user_ldp 9998f, \reg1, \reg2, \ptr, \val + user_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 1f61cd0df062..dbea3799c3ef 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 - user_ldst 9998f, ldtrh, \reg, \ptr, \val + user_ldst 9997f, ldtrh, \reg, \ptr, \val .endm .macro strh1 reg, ptr, val - user_ldst 9998f, sttrh, \reg, \ptr, \val + user_ldst 9997f, sttrh, \reg, \ptr, \val .endm .macro ldr1 reg, ptr, val - user_ldst 9998f, ldtr, \reg, \ptr, \val + user_ldst 9997f, ldtr, \reg, \ptr, \val .endm .macro str1 reg, ptr, val - user_ldst 9998f, sttr, \reg, \ptr, \val + user_ldst 9997f, sttr, \reg, \ptr, \val .endm .macro ldp1 reg1, reg2, ptr, val - user_ldp 9998f, \reg1, \reg2, \ptr, \val + user_ldp 9997f, \reg1, \reg2, \ptr, \val .endm .macro stp1 reg1, reg2, ptr, val - user_stp 9998f, \reg1, \reg2, \ptr, \val + user_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 043da90f5dd7..9f380eecf653 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 - user_ldst 9998f, sttrh, \reg, \ptr, \val + user_ldst 9997f, sttrh, \reg, \ptr, \val .endm .macro ldr1 reg, ptr, val @@ -40,7 +40,7 @@ .endm .macro str1 reg, ptr, val - user_ldst 9998f, sttr, \reg, \ptr, \val + user_ldst 9997f, sttr, \reg, \ptr, \val .endm .macro ldp1 reg1, reg2, ptr, val @@ -48,12 +48,14 @@ .endm .macro stp1 reg1, reg2, ptr, val - user_stp 9998f, \reg1, \reg2, \ptr, \val + user_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