linux-user/sh4/signal.c | 8 ++++++++ 1 file changed, 8 insertions(+)
sh4 uses gUSA (general UserSpace Atomicity) to provide atomicity on CPUs
that don't have atomic instructions. A gUSA region that adds 1 to an
atomic variable stored in @R2 looks like this:
4004b6: 03 c7 mova 4004c4 <gusa+0x10>,r0
4004b8: f3 61 mov r15,r1
4004ba: 09 00 nop
4004bc: fa ef mov #-6,r15
4004be: 22 63 mov.l @r2,r3
4004c0: 01 73 add #1,r3
4004c2: 32 22 mov.l r3,@r2
4004c4: 13 6f mov r1,r15
R0 contains a pointer to the end of the gUSA region
R1 contains the saved stack pointer
R15 contains negative length of the gUSA region
When this region is interrupted by a signal, the kernel detects if
R15 >= -128U. If yes, the kernel rolls back PC to the beginning of the
region and restores SP by copying R1 to R15.
The problem happens if we are interrupted by a signal at address 4004c4.
R15 still holds the value -6, but the atomic value was already written by
an instruction at address 4004c2. In this situation we can't undo the
gUSA. The function unwind_gusa does nothing, the signal handler attempts
to push a signal frame to the address -6 and crashes.
This patch fixes it, so that if we are interrupted at the last instruction
in a gUSA region, we copy R1 to R15 to restore the correct stack pointer
and avoid crashing.
There's another bug: if we are interrupted in a delay slot, we save the
address of the instruction in the delay slot. We must save the address of
the previous instruction.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: qemu-stable@nongnu.org
---
linux-user/sh4/signal.c | 8 ++++++++
1 file changed, 8 insertions(+)
Index: qemu/linux-user/sh4/signal.c
===================================================================
--- qemu.orig/linux-user/sh4/signal.c 2023-09-27 19:02:41.000000000 +0200
+++ qemu/linux-user/sh4/signal.c 2023-09-27 19:55:13.000000000 +0200
@@ -104,6 +104,14 @@ static void unwind_gusa(CPUSH4State *reg
/* Reset the SP to the saved version in R1. */
regs->gregs[15] = regs->gregs[1];
+ } else if (regs->gregs[15] >= -128u && regs->pc == regs->gregs[0]) {
+ /* If we are on the last instruction of a gUSA region, we must reset
+ the SP, otherwise we would be pushing the signal context to
+ invalid memory. */
+ regs->gregs[15] = regs->gregs[1];
+ } else if (regs->flags & TB_FLAG_DELAY_SLOT) {
+ /* If we are in a delay slot, push the previous instruction. */
+ regs->pc -= 2;
}
}On 9/28/23 09:42, Mikulas Patocka wrote: > sh4 uses gUSA (general UserSpace Atomicity) to provide atomicity on CPUs > that don't have atomic instructions. A gUSA region that adds 1 to an > atomic variable stored in @R2 looks like this: > > 4004b6: 03 c7 mova 4004c4 <gusa+0x10>,r0 > 4004b8: f3 61 mov r15,r1 > 4004ba: 09 00 nop > 4004bc: fa ef mov #-6,r15 > 4004be: 22 63 mov.l @r2,r3 > 4004c0: 01 73 add #1,r3 > 4004c2: 32 22 mov.l r3,@r2 > 4004c4: 13 6f mov r1,r15 > > R0 contains a pointer to the end of the gUSA region > R1 contains the saved stack pointer > R15 contains negative length of the gUSA region > > When this region is interrupted by a signal, the kernel detects if > R15 >= -128U. If yes, the kernel rolls back PC to the beginning of the > region and restores SP by copying R1 to R15. > > The problem happens if we are interrupted by a signal at address 4004c4. > R15 still holds the value -6, but the atomic value was already written by > an instruction at address 4004c2. In this situation we can't undo the > gUSA. The function unwind_gusa does nothing, the signal handler attempts > to push a signal frame to the address -6 and crashes. > > This patch fixes it, so that if we are interrupted at the last instruction > in a gUSA region, we copy R1 to R15 to restore the correct stack pointer > and avoid crashing. > > There's another bug: if we are interrupted in a delay slot, we save the > address of the instruction in the delay slot. We must save the address of > the previous instruction. > > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> > Cc: qemu-stable@nongnu.org > > --- > linux-user/sh4/signal.c | 8 ++++++++ > 1 file changed, 8 insertions(+) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Queued to linux-user-next. r~
On Fri, 29 Sep 2023 01:42:08 +0900,
Mikulas Patocka wrote:
>
> sh4 uses gUSA (general UserSpace Atomicity) to provide atomicity on CPUs
> that don't have atomic instructions. A gUSA region that adds 1 to an
> atomic variable stored in @R2 looks like this:
>
> 4004b6: 03 c7 mova 4004c4 <gusa+0x10>,r0
> 4004b8: f3 61 mov r15,r1
> 4004ba: 09 00 nop
> 4004bc: fa ef mov #-6,r15
> 4004be: 22 63 mov.l @r2,r3
> 4004c0: 01 73 add #1,r3
> 4004c2: 32 22 mov.l r3,@r2
> 4004c4: 13 6f mov r1,r15
>
> R0 contains a pointer to the end of the gUSA region
> R1 contains the saved stack pointer
> R15 contains negative length of the gUSA region
>
> When this region is interrupted by a signal, the kernel detects if
> R15 >= -128U. If yes, the kernel rolls back PC to the beginning of the
> region and restores SP by copying R1 to R15.
>
> The problem happens if we are interrupted by a signal at address 4004c4.
> R15 still holds the value -6, but the atomic value was already written by
> an instruction at address 4004c2. In this situation we can't undo the
> gUSA. The function unwind_gusa does nothing, the signal handler attempts
> to push a signal frame to the address -6 and crashes.
>
> This patch fixes it, so that if we are interrupted at the last instruction
> in a gUSA region, we copy R1 to R15 to restore the correct stack pointer
> and avoid crashing.
>
> There's another bug: if we are interrupted in a delay slot, we save the
> address of the instruction in the delay slot. We must save the address of
> the previous instruction.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: qemu-stable@nongnu.org
Reviewed-by: Yoshinori Sato <ysato@users.sourcefoege.jp>
> ---
> linux-user/sh4/signal.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> Index: qemu/linux-user/sh4/signal.c
> ===================================================================
> --- qemu.orig/linux-user/sh4/signal.c 2023-09-27 19:02:41.000000000 +0200
> +++ qemu/linux-user/sh4/signal.c 2023-09-27 19:55:13.000000000 +0200
> @@ -104,6 +104,14 @@ static void unwind_gusa(CPUSH4State *reg
>
> /* Reset the SP to the saved version in R1. */
> regs->gregs[15] = regs->gregs[1];
> + } else if (regs->gregs[15] >= -128u && regs->pc == regs->gregs[0]) {
> + /* If we are on the last instruction of a gUSA region, we must reset
> + the SP, otherwise we would be pushing the signal context to
> + invalid memory. */
> + regs->gregs[15] = regs->gregs[1];
> + } else if (regs->flags & TB_FLAG_DELAY_SLOT) {
> + /* If we are in a delay slot, push the previous instruction. */
> + regs->pc -= 2;
> }
> }
>
>
--
Yosinori Sato
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