* [PATCH 0/2] MIPS: memset.S: Fix 2 issues with __clear_user @ 2018-03-29 9:28 Matt Redfearn 2018-03-29 9:28 ` [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset Matt Redfearn 2018-03-29 9:28 ` [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup Matt Redfearn 0 siblings, 2 replies; 11+ messages in thread From: Matt Redfearn @ 2018-03-29 9:28 UTC (permalink / raw) To: James Hogan, Ralf Baechle; +Cc: linux-mips, Matt Redfearn, linux-kernel This series addresses 2 issues that have been present in memset.S since the initial git import(!). The first patch addresses an issue when memset is called with a size less than the size of a long (4 bytes on 32bit, 8 bytes on 64bit). There is no fixup handler provided for the byte store loop, meaning that if the access triggers a page fault, rather than being fixup up, the kernel OOPS'. A secondary issue is also addressed here, that when EVA support was added by commit fd9720e96e85 ("MIPS: lib: memset: Add EVA support for the __bzero function."), this small memset was not changed. Hence kernel mode addressing is always used and if the userspace address being stored to overlaps kernel, then some potentially critical kernel data is overwritten. The second patch addresses an issue found while debugging the first. clear_user() is specified to return the number of bytes that could not be cleared. After the first patch, this is now done for sizes 0-3, but sizes 4-63 would return garbage. This was tracked down to an error in reusing the t1 register meaning it no longer contained the expected value in the fault handler, and the fault handler erroneously masking off the lower bits of the result. The following test code was used to verify the behavior. int j, k; for (j = 0; j < 512; j++) { if ((k = clear_user(NULL, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } } Without patch 1, an OOPS is triggered by the first iteration. Without the second patch, j = 4..63 returns garbage. Applies on v4.16-rc7 Tested on MIPS creator ci40 (MIPS32) and Cavium Octeon II (MIPS64). Matt Redfearn (2): MIPS: memset.S: EVA & fault support for small_memset MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup arch/mips/lib/memset.S | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) -- 2.7.4 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset 2018-03-29 9:28 [PATCH 0/2] MIPS: memset.S: Fix 2 issues with __clear_user Matt Redfearn @ 2018-03-29 9:28 ` Matt Redfearn 2018-04-16 20:22 ` James Hogan 2018-03-29 9:28 ` [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup Matt Redfearn 1 sibling, 1 reply; 11+ messages in thread From: Matt Redfearn @ 2018-03-29 9:28 UTC (permalink / raw) To: James Hogan, Ralf Baechle; +Cc: linux-mips, Matt Redfearn, stable, linux-kernel The MIPS kernel memset / bzero implementation includes a small_memset branch which is used when the region to be set is smaller than a long (4 bytes on 32bit, 8 bytes on 64bit). The current small_memset implementation uses a simple store byte loop to write the destination. There are 2 issues with this implementation: 1. When EVA mode is active, user and kernel address spaces may overlap. Currently the use of the sb instruction means kernel mode addressing is always used and an intended write to userspace may actually overwrite some critical kernel data. 2. If the write triggers a page fault, for example by calling __clear_user(NULL, 2), instead of gracefully handling the fault, an OOPS is triggered. Fix these issues by replacing the sb instruction with the EX() macro, which will emit EVA compatible instuctions as required. Additionally implement a fault fixup for small_memset which sets a2 to the number of bytes that could not be cleared (as defined by __clear_user). Reported-by: Chuanhua Lei <chuanhua.lei@intel.com> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> --- arch/mips/lib/memset.S | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index a1456664d6c2..90bcdf1224ee 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -219,7 +219,7 @@ 1: PTR_ADDIU a0, 1 /* fill bytewise */ R10KCBARRIER(0(ra)) bne t1, a0, 1b - sb a1, -1(a0) + EX(sb, a1, -1(a0), .Lsmall_fixup\@) 2: jr ra /* done */ move a2, zero @@ -260,6 +260,11 @@ jr ra andi v1, a2, STORMASK +.Lsmall_fixup\@: + PTR_SUBU a2, t1, a0 + jr ra + PTR_ADDIU a2, 1 + .endm /* -- 2.7.4 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset 2018-03-29 9:28 ` [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset Matt Redfearn @ 2018-04-16 20:22 ` James Hogan 2018-04-17 13:20 ` Matt Redfearn 2018-05-14 22:56 ` Maciej W. Rozycki 0 siblings, 2 replies; 11+ messages in thread From: James Hogan @ 2018-04-16 20:22 UTC (permalink / raw) To: Matt Redfearn; +Cc: Ralf Baechle, linux-mips, stable, linux-kernel [-- Attachment #1: Type: text/plain, Size: 417 bytes --] On Thu, Mar 29, 2018 at 10:28:23AM +0100, Matt Redfearn wrote: > @@ -260,6 +260,11 @@ > jr ra > andi v1, a2, STORMASK This patch looks good, well spotted! But whats that v1 write about? Any ideas? Seems to go back to the git epoch, and $3 isn't in the clobber lists when __bzero* is called. Cheers James > > +.Lsmall_fixup\@: > + PTR_SUBU a2, t1, a0 > + jr ra > + PTR_ADDIU a2, 1 > + [-- Attachment #2: Digital signature --] [-- Type: application/pgp-signature, Size: 833 bytes --] ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset 2018-04-16 20:22 ` James Hogan @ 2018-04-17 13:20 ` Matt Redfearn 2018-05-14 22:56 ` Maciej W. Rozycki 1 sibling, 0 replies; 11+ messages in thread From: Matt Redfearn @ 2018-04-17 13:20 UTC (permalink / raw) To: James Hogan; +Cc: Ralf Baechle, linux-mips, stable, linux-kernel Hi James, On 16/04/18 21:22, James Hogan wrote: > On Thu, Mar 29, 2018 at 10:28:23AM +0100, Matt Redfearn wrote: >> @@ -260,6 +260,11 @@ >> jr ra >> andi v1, a2, STORMASK > > This patch looks good, well spotted! > > But whats that v1 write about? Any ideas? Seems to go back to the git > epoch, and $3 isn't in the clobber lists when __bzero* is called. No idea what the original intent was, but I've verified that v1 does indeed get clobbered if this path is hit. Patch incoming! Thanks, Matt > > Cheers > James > >> >> +.Lsmall_fixup\@: >> + PTR_SUBU a2, t1, a0 >> + jr ra >> + PTR_ADDIU a2, 1 >> + ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset 2018-04-16 20:22 ` James Hogan 2018-04-17 13:20 ` Matt Redfearn @ 2018-05-14 22:56 ` Maciej W. Rozycki 1 sibling, 0 replies; 11+ messages in thread From: Maciej W. Rozycki @ 2018-05-14 22:56 UTC (permalink / raw) To: James Hogan; +Cc: Matt Redfearn, Ralf Baechle, linux-mips, stable, linux-kernel On Mon, 16 Apr 2018, James Hogan wrote: > > @@ -260,6 +260,11 @@ > > jr ra > > andi v1, a2, STORMASK > > This patch looks good, well spotted! > > But whats that v1 write about? Any ideas? Seems to go back to the git > epoch, and $3 isn't in the clobber lists when __bzero* is called. You need to dive deeper, that is beyond the secret commit 66f0a432564b ("Add resource managment."), to find what's happened before the epoch. ;) Anyway, there isn't anything special here, the thing has been here since the inception of memset.S with commit 2e0f55e79c49 (no shortlog available for that one). And it is clearly a bug, possibly just a leftover from a WIP implementation or whatever. And I can see Matt has already fixed that, thanks! Maciej ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-03-29 9:28 [PATCH 0/2] MIPS: memset.S: Fix 2 issues with __clear_user Matt Redfearn 2018-03-29 9:28 ` [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset Matt Redfearn @ 2018-03-29 9:28 ` Matt Redfearn 2018-04-16 22:13 ` James Hogan 1 sibling, 1 reply; 11+ messages in thread From: Matt Redfearn @ 2018-03-29 9:28 UTC (permalink / raw) To: James Hogan, Ralf Baechle; +Cc: linux-mips, Matt Redfearn, stable, linux-kernel The __clear_user function is defined to return the number of bytes that could not be cleared. From the underlying memset / bzero implementation this means setting register a2 to that number on return. Currently if a page fault is triggered within the memset_partial block, the value loaded into a2 on return is meaningless. The label .Lpartial_fixup\@ is jumped to on page fault. Currently it masks the remaining count of bytes (a2) with STORMASK, meaning that the least significant 2 (32bit) or 3 (64bit) bits of the remaining count are always clear. Secondly, .Lpartial_fixup\@ expects t1 to contain the end address of the copy. This is set up by the initial block: PTR_ADDU t1, a0 /* end address */ However, the .Lmemset_partial\@ block then reuses register t1 to calculate a jump through a block of word copies. This leaves it no longer containing the end address of the copy operation if a page fault occurs, and the remaining bytes calculation is incorrect. Fix these issues by removing the and of a2 with STORMASK, and replace t1 with register t2 in the .Lmemset_partial\@ block. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> --- arch/mips/lib/memset.S | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 90bcdf1224ee..3257dca58cad 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -161,19 +161,19 @@ .Lmemset_partial\@: R10KCBARRIER(0(ra)) - PTR_LA t1, 2f /* where to start */ + PTR_LA t2, 2f /* where to start */ #ifdef CONFIG_CPU_MICROMIPS LONG_SRL t7, t0, 1 #endif #if LONGSIZE == 4 - PTR_SUBU t1, FILLPTRG + PTR_SUBU t2, FILLPTRG #else .set noat LONG_SRL AT, FILLPTRG, 1 - PTR_SUBU t1, AT + PTR_SUBU t2, AT .set at #endif - jr t1 + jr t2 PTR_ADDU a0, t0 /* dest ptr */ .set push @@ -250,7 +250,6 @@ .Lpartial_fixup\@: PTR_L t0, TI_TASK($28) - andi a2, STORMASK LONG_L t0, THREAD_BUADDR(t0) LONG_ADDU a2, t1 jr ra -- 2.7.4 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-03-29 9:28 ` [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup Matt Redfearn @ 2018-04-16 22:13 ` James Hogan 2018-04-17 13:21 ` Matt Redfearn 2018-04-17 13:59 ` [PATCH v2] " Matt Redfearn 0 siblings, 2 replies; 11+ messages in thread From: James Hogan @ 2018-04-16 22:13 UTC (permalink / raw) To: Matt Redfearn; +Cc: Ralf Baechle, linux-mips, stable, linux-kernel [-- Attachment #1: Type: text/plain, Size: 3741 bytes --] On Thu, Mar 29, 2018 at 10:28:24AM +0100, Matt Redfearn wrote: > The __clear_user function is defined to return the number of bytes that > could not be cleared. From the underlying memset / bzero implementation > this means setting register a2 to that number on return. Currently if a > page fault is triggered within the memset_partial block, the value > loaded into a2 on return is meaningless. > > The label .Lpartial_fixup\@ is jumped to on page fault. Currently it > masks the remaining count of bytes (a2) with STORMASK, meaning that the > least significant 2 (32bit) or 3 (64bit) bits of the remaining count are > always clear. Are you sure about that. It seems to do that *to ensure those bits are set correctly*... > Secondly, .Lpartial_fixup\@ expects t1 to contain the end address of the > copy. This is set up by the initial block: > PTR_ADDU t1, a0 /* end address */ > However, the .Lmemset_partial\@ block then reuses register t1 to > calculate a jump through a block of word copies. This leaves it no > longer containing the end address of the copy operation if a page fault > occurs, and the remaining bytes calculation is incorrect. > > Fix these issues by removing the and of a2 with STORMASK, and replace t1 > with register t2 in the .Lmemset_partial\@ block. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org > Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> > --- > > arch/mips/lib/memset.S | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S > index 90bcdf1224ee..3257dca58cad 100644 > --- a/arch/mips/lib/memset.S > +++ b/arch/mips/lib/memset.S > @@ -161,19 +161,19 @@ > > .Lmemset_partial\@: > R10KCBARRIER(0(ra)) > - PTR_LA t1, 2f /* where to start */ > + PTR_LA t2, 2f /* where to start */ > #ifdef CONFIG_CPU_MICROMIPS > LONG_SRL t7, t0, 1 Hmm, on microMIPS t7 isn't on the clobber list for __bzero, and nor is t8... > #endif > #if LONGSIZE == 4 > - PTR_SUBU t1, FILLPTRG > + PTR_SUBU t2, FILLPTRG > #else > .set noat > LONG_SRL AT, FILLPTRG, 1 > - PTR_SUBU t1, AT > + PTR_SUBU t2, AT > .set at > #endif > - jr t1 > + jr t2 > PTR_ADDU a0, t0 /* dest ptr */ ^^^ note this... > > .set push > @@ -250,7 +250,6 @@ > > .Lpartial_fixup\@: > PTR_L t0, TI_TASK($28) > - andi a2, STORMASK ... this isn't right. If I read correctly, t1 (after the above change stops clobbering it) is the end of the full 64-byte blocks, i.e. the start address of the final partial block. The .Lfwd_fixup calculation (for full blocks) appears to be: a2 = ((len & 0x3f) + start_of_partial) - badvaddr which is spot on. (len & 0x3f) is the partial block and remaining bytes that haven't been set yet, add start_of_partial to get end of the full range, subtract bad address to find how much didn't copy. The calculation for .Lpartial_fixup however appears to (currently) do: a2 = ((len & STORMASK) + start_of_partial) - badvaddr Which might make sense if start_of_partial (t1) was replaced with end_of_partial, which does seem to be calculated as noted above, and put in a0 ready for the final few bytes to be set. > LONG_L t0, THREAD_BUADDR(t0) > LONG_ADDU a2, t1 ^^ So I think either it needs to just s/t1/a0/ here and not bother preserving t1 above (smaller change and probably the original intent), or preserve t1 and mask 0x3f instead of STORMASK like .Lfwd_fixup does (which would work but seems needlessly complicated to me). Does that make any sense or have I misunderstood some subtlety? Cheers James > jr ra > -- > 2.7.4 > [-- Attachment #2: Digital signature --] [-- Type: application/pgp-signature, Size: 833 bytes --] ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-04-16 22:13 ` James Hogan @ 2018-04-17 13:21 ` Matt Redfearn 2018-04-17 13:59 ` [PATCH v2] " Matt Redfearn 1 sibling, 0 replies; 11+ messages in thread From: Matt Redfearn @ 2018-04-17 13:21 UTC (permalink / raw) To: James Hogan; +Cc: Ralf Baechle, linux-mips, stable, linux-kernel Hi James, On 16/04/18 23:13, James Hogan wrote: > On Thu, Mar 29, 2018 at 10:28:24AM +0100, Matt Redfearn wrote: >> The __clear_user function is defined to return the number of bytes that >> could not be cleared. From the underlying memset / bzero implementation >> this means setting register a2 to that number on return. Currently if a >> page fault is triggered within the memset_partial block, the value >> loaded into a2 on return is meaningless. >> >> The label .Lpartial_fixup\@ is jumped to on page fault. Currently it >> masks the remaining count of bytes (a2) with STORMASK, meaning that the >> least significant 2 (32bit) or 3 (64bit) bits of the remaining count are >> always clear. > > Are you sure about that. It seems to do that *to ensure those bits are > set correctly*... > >> Secondly, .Lpartial_fixup\@ expects t1 to contain the end address of the >> copy. This is set up by the initial block: >> PTR_ADDU t1, a0 /* end address */ >> However, the .Lmemset_partial\@ block then reuses register t1 to >> calculate a jump through a block of word copies. This leaves it no >> longer containing the end address of the copy operation if a page fault >> occurs, and the remaining bytes calculation is incorrect. >> >> Fix these issues by removing the and of a2 with STORMASK, and replace t1 >> with register t2 in the .Lmemset_partial\@ block. >> >> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") >> Cc: stable@vger.kernel.org >> Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> >> --- >> >> arch/mips/lib/memset.S | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S >> index 90bcdf1224ee..3257dca58cad 100644 >> --- a/arch/mips/lib/memset.S >> +++ b/arch/mips/lib/memset.S >> @@ -161,19 +161,19 @@ >> >> .Lmemset_partial\@: >> R10KCBARRIER(0(ra)) >> - PTR_LA t1, 2f /* where to start */ >> + PTR_LA t2, 2f /* where to start */ >> #ifdef CONFIG_CPU_MICROMIPS >> LONG_SRL t7, t0, 1 > > Hmm, on microMIPS t7 isn't on the clobber list for __bzero, and nor is > t8... > >> #endif >> #if LONGSIZE == 4 >> - PTR_SUBU t1, FILLPTRG >> + PTR_SUBU t2, FILLPTRG >> #else >> .set noat >> LONG_SRL AT, FILLPTRG, 1 >> - PTR_SUBU t1, AT >> + PTR_SUBU t2, AT >> .set at >> #endif >> - jr t1 >> + jr t2 >> PTR_ADDU a0, t0 /* dest ptr */ > > ^^^ note this... > >> >> .set push >> @@ -250,7 +250,6 @@ >> >> .Lpartial_fixup\@: >> PTR_L t0, TI_TASK($28) >> - andi a2, STORMASK > > ... this isn't right. > > If I read correctly, t1 (after the above change stops clobbering it) is > the end of the full 64-byte blocks, i.e. the start address of the final > partial block. > > > The .Lfwd_fixup calculation (for full blocks) appears to be: > > a2 = ((len & 0x3f) + start_of_partial) - badvaddr > > which is spot on. (len & 0x3f) is the partial block and remaining bytes > that haven't been set yet, add start_of_partial to get end of the full > range, subtract bad address to find how much didn't copy. > > > The calculation for .Lpartial_fixup however appears to (currently) do: > > a2 = ((len & STORMASK) + start_of_partial) - badvaddr > > Which might make sense if start_of_partial (t1) was replaced with > end_of_partial, which does seem to be calculated as noted above, and put > in a0 ready for the final few bytes to be set. > >> LONG_L t0, THREAD_BUADDR(t0) >> LONG_ADDU a2, t1 > > ^^ So I think either it needs to just s/t1/a0/ here and not bother > preserving t1 above (smaller change and probably the original intent), > or preserve t1 and mask 0x3f instead of STORMASK like .Lfwd_fixup does > (which would work but seems needlessly complicated to me). > > Does that make any sense or have I misunderstood some subtlety? Thanks for taking the time to work this through - you're right, changing t1 to a0 in the fault handler does give the right result and is much less invasive. Updated patch incoming :-) Thanks, Matt > > Cheers > James > >> jr ra >> -- >> 2.7.4 >> ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-04-16 22:13 ` James Hogan 2018-04-17 13:21 ` Matt Redfearn @ 2018-04-17 13:59 ` Matt Redfearn 2018-04-17 14:52 ` [PATCH v3] " Matt Redfearn 1 sibling, 1 reply; 11+ messages in thread From: Matt Redfearn @ 2018-04-17 13:59 UTC (permalink / raw) To: James Hogan, Ralf Baechle; +Cc: linux-mips, Matt Redfearn, stable, linux-kernel The __clear_user function is defined to return the number of bytes that could not be cleared. From the underlying memset / bzero implementation this means setting register a2 to that number on return. Currently if a page fault is triggered within the memset_partial block, the value loaded into a2 on return is meaningless. The label .Lpartial_fixup\@ is jumped to on page fault. In order to work out how many bytes failed to copy, the exception handler should find how many bytes left in the partial block (andi a2, STORMASK), add that to the partial block end address (a2), and subtract the faulting address to get the remainder. Currently it incorrectly subtracts the partial block start address (t1), which has additionally has been clobbered to generate a jump target in memset_partial. Fix this by adding the block end address instead. Since this code is non-trivial to read, add comments to describe the fault handling. This issue was found with the following test code: int j, k; for (j = 0; j < 512; j++) { if ((k = clear_user(NULL, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } } Which now passes on Creator Ci40 (MIPS32) and Cavium Octeon II (MIPS64). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Suggested-by: James Hogan <jhogan@kernel.org> Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> --- Changes in v2: - Use James Hogan's suggestion of replacing t1 with a0 to get the correct remainder count. - Add comments to .Lpartial_fixup to aid those who next try to deciper this code. arch/mips/lib/memset.S | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 90bcdf1224ee..fa3bec269331 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -250,11 +250,11 @@ .Lpartial_fixup\@: PTR_L t0, TI_TASK($28) - andi a2, STORMASK - LONG_L t0, THREAD_BUADDR(t0) - LONG_ADDU a2, t1 + andi a2, STORMASK /* #Bytes beyond partial block */ + LONG_L t0, THREAD_BUADDR(t0) /* Get faulting address */ + LONG_ADDU a2, a0 /* Add end address of partial block */ jr ra - LONG_SUBU a2, t0 + LONG_SUBU a2, t0 /* a2 = partial_end + #bytes - fault */ .Llast_fixup\@: jr ra -- 2.7.4 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* [PATCH v3] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-04-17 13:59 ` [PATCH v2] " Matt Redfearn @ 2018-04-17 14:52 ` Matt Redfearn 2018-04-17 15:43 ` James Hogan 0 siblings, 1 reply; 11+ messages in thread From: Matt Redfearn @ 2018-04-17 14:52 UTC (permalink / raw) To: James Hogan, Ralf Baechle; +Cc: linux-mips, Matt Redfearn, stable, linux-kernel The __clear_user function is defined to return the number of bytes that could not be cleared. From the underlying memset / bzero implementation this means setting register a2 to that number on return. Currently if a page fault is triggered within the memset_partial block, the value loaded into a2 on return is meaningless. The label .Lpartial_fixup\@ is jumped to on page fault. In order to work out how many bytes failed to copy, the exception handler should find how many bytes left in the partial block (andi a2, STORMASK), add that to the partial block end address (a2), and subtract the faulting address to get the remainder. Currently it incorrectly subtracts the partial block start address (t1), which has additionally has been clobbered to generate a jump target in memset_partial. Fix this by adding the block end address instead. This issue was found with the following test code: int j, k; for (j = 0; j < 512; j++) { if ((k = clear_user(NULL, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } } Which now passes on Creator Ci40 (MIPS32) and Cavium Octeon II (MIPS64). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Suggested-by: James Hogan <jhogan@kernel.org> Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> --- Changes in v3: - Just fix the issue at hand Changes in v2: - Use James Hogan's suggestion of replacing t1 with a0 to get the correct remainder count. arch/mips/lib/memset.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 90bcdf1224ee..184819c1d5c8 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -252,7 +252,7 @@ PTR_L t0, TI_TASK($28) andi a2, STORMASK LONG_L t0, THREAD_BUADDR(t0) - LONG_ADDU a2, t1 + LONG_ADDU a2, a0 jr ra LONG_SUBU a2, t0 -- 2.7.4 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v3] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup 2018-04-17 14:52 ` [PATCH v3] " Matt Redfearn @ 2018-04-17 15:43 ` James Hogan 0 siblings, 0 replies; 11+ messages in thread From: James Hogan @ 2018-04-17 15:43 UTC (permalink / raw) To: Matt Redfearn; +Cc: Ralf Baechle, linux-mips, stable, linux-kernel [-- Attachment #1: Type: text/plain, Size: 1488 bytes --] On Tue, Apr 17, 2018 at 03:52:21PM +0100, Matt Redfearn wrote: > The __clear_user function is defined to return the number of bytes that > could not be cleared. From the underlying memset / bzero implementation > this means setting register a2 to that number on return. Currently if a > page fault is triggered within the memset_partial block, the value > loaded into a2 on return is meaningless. > > The label .Lpartial_fixup\@ is jumped to on page fault. In order to work > out how many bytes failed to copy, the exception handler should find how > many bytes left in the partial block (andi a2, STORMASK), add that to > the partial block end address (a2), and subtract the faulting address to > get the remainder. Currently it incorrectly subtracts the partial block > start address (t1), which has additionally has been clobbered to > generate a jump target in memset_partial. Fix this by adding the block > end address instead. > > This issue was found with the following test code: > int j, k; > for (j = 0; j < 512; j++) { > if ((k = clear_user(NULL, j)) != j) { > pr_err("clear_user (NULL %d) returned %d\n", j, k); > } > } > Which now passes on Creator Ci40 (MIPS32) and Cavium Octeon II (MIPS64). > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org > Suggested-by: James Hogan <jhogan@kernel.org> > Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> Applied, thanks James [-- Attachment #2: Digital signature --] [-- Type: application/pgp-signature, Size: 833 bytes --] ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2018-05-14 23:11 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-03-29 9:28 [PATCH 0/2] MIPS: memset.S: Fix 2 issues with __clear_user Matt Redfearn 2018-03-29 9:28 ` [PATCH 1/2] MIPS: memset.S: EVA & fault support for small_memset Matt Redfearn 2018-04-16 20:22 ` James Hogan 2018-04-17 13:20 ` Matt Redfearn 2018-05-14 22:56 ` Maciej W. Rozycki 2018-03-29 9:28 ` [PATCH 2/2] MIPS: memset.S: Fix return of __clear_user from Lpartial_fixup Matt Redfearn 2018-04-16 22:13 ` James Hogan 2018-04-17 13:21 ` Matt Redfearn 2018-04-17 13:59 ` [PATCH v2] " Matt Redfearn 2018-04-17 14:52 ` [PATCH v3] " Matt Redfearn 2018-04-17 15:43 ` James Hogan
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