From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Guenter Roeck <linux@roeck-us.net>,
x86@kernel.org, linux-kernel@vger.kernel.org,
jpoimboe@redhat.com, brgerst@gmail.com, jiangshanlai@gmail.com,
Andrew.Cooper3@citrix.com, mark.rutland@arm.com,
Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat
Date: Thu, 19 May 2022 10:11:29 -0700 [thread overview]
Message-ID: <20220519171129.enw32izjhxsqc2xm@treble> (raw)
In-Reply-To: <20220519170009.GL2578@worktop.programming.kicks-ass.net>
On Thu, May 19, 2022 at 07:00:09PM +0200, Peter Zijlstra wrote:
> On Thu, May 19, 2022 at 09:24:11AM -0700, Guenter Roeck wrote:
> > On Fri, May 06, 2022 at 02:14:34PM +0200, Peter Zijlstra wrote:
> > > Since the upper regs don't exist for ia32 code, preserving them
> > > doesn't hurt and it simplifies the code.
> > >
> > > This doesn't add any attack surface that would not already be
> > > available through INT80.
> > >
> > > Notably:
> > >
> > > - 32bit SYSENTER: didn't clear si, dx, cx.
> > >
> > > - 32bit SYSCALL, INT80: *do* clear si since the C functions don't
> > > take a second argument.
> > >
> > > - 64bit: didn't clear si since the C functions take a second
> > > argument; except the error_entry path might have only one argument,
> > > so clearing si was missing here.
> > >
> > > 32b SYSENTER should be clearing all those 3 registers, nothing uses them
> > > and selftests pass.
> > >
> > > Unconditionally clear rsi since it simplifies code.
> > >
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Reviewed-by: Borislav Petkov <bp@suse.de>
> >
> > linux-next (next-20220519) crashes due to this patch when booting
> > q35:EPYC-Rome in qemu.
>
> Could you try backing out each of the hunks one at a time? They're all
> more or less independent.
>
> My bet with this being a #PF on an AMD machine, it's either the SI clear
> or the SYSCALL change.
I think this should fix it:
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index a97cc78ecb92..29b36e9e4e74 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -63,7 +63,7 @@ For 32-bit we have the following conventions - kernel is built with
* for assembly code:
*/
-.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0
+.macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0
.if \save_ret
pushq %rsi /* pt_regs->si */
movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */
@@ -73,7 +73,7 @@ For 32-bit we have the following conventions - kernel is built with
pushq %rsi /* pt_regs->si */
.endif
pushq \rdx /* pt_regs->dx */
- pushq %rcx /* pt_regs->cx */
+ pushq \rcx /* pt_regs->cx */
pushq \rax /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 */
pushq %r9 /* pt_regs->r9 */
@@ -115,8 +115,8 @@ For 32-bit we have the following conventions - kernel is built with
.endm
-.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
- PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret
+.macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0
+ PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret
CLEAR_REGS
.endm
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index ed2be3615b50..2d40dd132442 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -200,7 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
movl %eax, %eax /* discard orig_ax high bits */
pushq %rax /* pt_regs->orig_ax */
- PUSH_AND_CLEAR_REGS rax=$-ENOSYS
+ PUSH_AND_CLEAR_REGS rax=$-ENOSYS rcx=%rbx
UNWIND_HINT_REGS
movq %rsp, %rdi
next prev parent reply other threads:[~2022-05-19 17:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-06 12:14 [PATCH 0/6] x86: Various cleanups and fixes Peter Zijlstra
2022-05-06 12:14 ` [PATCH 1/6] x86/mm: Simplify RESERVE_BRK() Peter Zijlstra
2022-05-06 15:09 ` [tip: x86/asm] " tip-bot2 for Josh Poimboeuf
2022-05-06 12:14 ` [PATCH 2/6] x86/entry: Simplify entry_INT80_compat() Peter Zijlstra
2022-05-06 15:09 ` [tip: x86/asm] " tip-bot2 for Linus Torvalds
2022-05-06 12:14 ` [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat Peter Zijlstra
2022-05-06 15:09 ` [tip: x86/asm] " tip-bot2 for Peter Zijlstra
2022-05-07 2:54 ` [PATCH 3/6] " Lai Jiangshan
2022-05-19 16:24 ` Guenter Roeck
2022-05-19 17:00 ` Peter Zijlstra
2022-05-19 17:11 ` Josh Poimboeuf [this message]
2022-05-19 17:35 ` Josh Poimboeuf
2022-05-20 1:11 ` Lai Jiangshan
2022-05-20 2:46 ` Guenter Roeck
2022-05-20 15:55 ` Josh Poimboeuf
2022-05-06 12:14 ` [PATCH 4/6] x86/entry: Remove skip_r11rcx Peter Zijlstra
2022-05-06 15:09 ` [tip: x86/asm] " tip-bot2 for Peter Zijlstra
2022-05-07 2:52 ` [PATCH 4/6] " Lai Jiangshan
2022-05-06 12:14 ` [PATCH 5/6] linkage: Fix issue with missing symbol size Peter Zijlstra
2022-05-06 15:08 ` [tip: x86/asm] " tip-bot2 for Peter Zijlstra
2022-05-06 12:14 ` [PATCH 6/6] objtool: Fix STACK_FRAME_NON_STANDARD reloc type Peter Zijlstra
2022-05-06 15:08 ` [tip: x86/asm] " tip-bot2 for Peter Zijlstra
2022-05-06 16:05 ` [PATCH 6/6] " Josh Poimboeuf
2022-05-06 20:26 ` [tip: x86/asm] " tip-bot2 for Peter Zijlstra
2022-05-19 18:31 [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat Guenter Roeck
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