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| Started by | Andy Lutomirski <luto@amacapital.net> |
|---|---|
| First post | 2015-08-31 23:10 +0200 |
| Last post | 2015-09-01 23:50 +0200 |
| Articles | 5 — 2 participants |
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Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-08-31 23:10 +0200
Re: Why is irq_stack_union a union? Brian Gerst <brgerst@gmail.com> - 2015-08-31 23:50 +0200
Re: Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-09-01 00:10 +0200
Re: Why is irq_stack_union a union? Brian Gerst <brgerst@gmail.com> - 2015-09-01 06:00 +0200
Re: Why is irq_stack_union a union? Andy Lutomirski <luto@amacapital.net> - 2015-09-01 23:50 +0200
| From | Andy Lutomirski <luto@amacapital.net> |
|---|---|
| Date | 2015-08-31 23:10 +0200 |
| Subject | Why is irq_stack_union a union? |
| Message-ID | <q3Ev1-2yp-23@gated-at.bofh.it> |
Why not just a struct? Also, why is this all tangled up in gsbase initialization? And why does irq_stack_ptr point 64 bytes from the top? And why does the stack overflow thing look STACK_TOP_MARGIN == 128 bytes from the top? Confused. --Andy -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Brian Gerst <brgerst@gmail.com> |
|---|---|
| Date | 2015-08-31 23:50 +0200 |
| Message-ID | <q3F7H-3hD-3@gated-at.bofh.it> |
| In reply to | #1216450 |
On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote: > Why not just a struct? Also, why is this all tangled up in gsbase initialization? It has to do with the fact that the GCC stackprotector is hardcoded to look for the canary at %gs:40. Since we also use %gs for the percpu segment, we have to make sure that the canary is placed at the start of the percpu section. Overlaying it onto the bottom of the IRQ stack and was the most convenient way to do it, with a side benefit that overflowing the stack will trip the canary. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Andy Lutomirski <luto@amacapital.net> |
|---|---|
| Date | 2015-09-01 00:10 +0200 |
| Message-ID | <q3Fr3-3Tm-9@gated-at.bofh.it> |
| In reply to | #1216473 |
On Mon, Aug 31, 2015 at 2:47 PM, Brian Gerst <brgerst@gmail.com> wrote: > On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote: >> Why not just a struct? Also, why is this all tangled up in gsbase initialization? > > It has to do with the fact that the GCC stackprotector is hardcoded to > look for the canary at %gs:40. Since we also use %gs for the percpu > segment, we have to make sure that the canary is placed at the start > of the percpu section. Overlaying it onto the bottom of the IRQ stack > and was the most convenient way to do it, with a side benefit that > overflowing the stack will trip the canary. Would a struct not make more sense, then? --Andy > > -- > Brian Gerst -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Brian Gerst <brgerst@gmail.com> |
|---|---|
| Date | 2015-09-01 06:00 +0200 |
| Message-ID | <q3KTM-3lU-1@gated-at.bofh.it> |
| In reply to | #1216480 |
On Mon, Aug 31, 2015 at 6:01 PM, Andy Lutomirski <luto@amacapital.net> wrote: > On Mon, Aug 31, 2015 at 2:47 PM, Brian Gerst <brgerst@gmail.com> wrote: >> On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote: >>> Why not just a struct? Also, why is this all tangled up in gsbase initialization? >> >> It has to do with the fact that the GCC stackprotector is hardcoded to >> look for the canary at %gs:40. Since we also use %gs for the percpu >> segment, we have to make sure that the canary is placed at the start >> of the percpu section. Overlaying it onto the bottom of the IRQ stack >> and was the most convenient way to do it, with a side benefit that >> overflowing the stack will trip the canary. > > Would a struct not make more sense, then? Why would it? A union shows the overlay better. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Andy Lutomirski <luto@amacapital.net> |
|---|---|
| Date | 2015-09-01 23:50 +0200 |
| Message-ID | <q41Bf-21v-3@gated-at.bofh.it> |
| In reply to | #1216578 |
On Mon, Aug 31, 2015 at 8:55 PM, Brian Gerst <brgerst@gmail.com> wrote: > On Mon, Aug 31, 2015 at 6:01 PM, Andy Lutomirski <luto@amacapital.net> wrote: >> On Mon, Aug 31, 2015 at 2:47 PM, Brian Gerst <brgerst@gmail.com> wrote: >>> On Mon, Aug 31, 2015 at 5:00 PM, Andy Lutomirski <luto@amacapital.net> wrote: >>>> Why not just a struct? Also, why is this all tangled up in gsbase initialization? >>> >>> It has to do with the fact that the GCC stackprotector is hardcoded to >>> look for the canary at %gs:40. Since we also use %gs for the percpu >>> segment, we have to make sure that the canary is placed at the start >>> of the percpu section. Overlaying it onto the bottom of the IRQ stack >>> and was the most convenient way to do it, with a side benefit that >>> overflowing the stack will trip the canary. >> >> Would a struct not make more sense, then? > > Why would it? A union shows the overlay better. I guess you're thinking of it as an overlay and I'm thinking of it as the layout being the IRQ stack directly above the stack canary. --Andy > > -- > Brian Gerst -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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