Messages in this thread | | | Subject | Re: [PATCH v2 4/4] MIPS: memset.S: Add comments to fault fixup handlers | From | Matt Redfearn <> | Date | Tue, 22 May 2018 13:20:58 +0100 |
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Hi James,
On 21/05/18 17:14, James Hogan wrote: > On Tue, Apr 17, 2018 at 04:40:03PM +0100, Matt Redfearn wrote: >> diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S >> index 1cc306520a55..a06dabe99d4b 100644 >> --- a/arch/mips/lib/memset.S >> +++ b/arch/mips/lib/memset.S >> @@ -231,16 +231,25 @@ >> >> #ifdef CONFIG_CPU_MIPSR6 >> .Lbyte_fixup\@: >> + /* >> + * unset_bytes = current_addr + 1 >> + * a2 = t0 + 1 > > The code looks more like a2 = 1 - t0 to me: > >> + */ >> PTR_SUBU a2, $0, t0 >> jr ra >> PTR_ADDIU a2, 1 > > I.e. t0 counts up to 1 and then stops.
Well spotted. Which means this code is also wrong.... :-/
We have the count of bytes to zero in a2, but that gets clobbered in the exception handler and we always return a number of bytes uncopied within STORSIZE.
This test code:
static int __init __attribute__((optimize("O0"))) test_clear_user(void) { int j, k;
pr_info("\n\n\nTesting clear_user\n");
for (j = 0; j < 512; j++) { if ((k = clear_user(NULL+3, j)) != j) { pr_err("clear_user (NULL %d) returned %d\n", j, k); } }
return 0; } late_initcall(test_clear_user);
on a 64r6el kernel results in:
[ 3.965439] Testing clear_user [ 3.973169] clear_user (NULL 8) returned 6 [ 3.976782] clear_user (NULL 9) returned 6 [ 3.980390] clear_user (NULL 10) returned 6 [ 3.984052] clear_user (NULL 11) returned 6 [ 3.987524] clear_user (NULL 12) returned 6 [ 3.991179] clear_user (NULL 13) returned 6 [ 3.994841] clear_user (NULL 14) returned 6 [ 3.998500] clear_user (NULL 15) returned 6 [ 4.002160] clear_user (NULL 16) returned 6 [ 4.005820] clear_user (NULL 17) returned 6 [ 4.009480] clear_user (NULL 18) returned 6 [ 4.013140] clear_user (NULL 19) returned 6 [ 4.016797] clear_user (NULL 20) returned 6 [ 4.020456] clear_user (NULL 21) returned 6
I'll post another fix soon, and update this comment to reflect the corrected behavior.
Thanks, Matt
> > Anyway I've applied patch 3 for 4.18. > > Cheers > James >
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