Messages in this thread Patch in this message | | | Subject | Re: [PATCH] x86/entry/32: Fix setup of CS high bits | From | Jan Kiszka <> | Date | Mon, 15 Oct 2018 15:08:54 +0200 |
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On 13.10.18 17:12, Andy Lutomirski wrote: > On Sat, Oct 13, 2018 at 3:02 AM Jan Kiszka <jan.kiszka@web.de> wrote: >> >> From: Jan Kiszka <jan.kiszka@siemens.com> >> >> Even if we are not on an entry stack, we have to initialize the CS high >> bits because we are unconditionally evaluating them >> PARANOID_EXIT_TO_KERNEL_MODE. Failing to do so broke the boot on Galileo >> Gen2 and IOT2000 boards. >> >> Fixes: b92a165df17e ("x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack") >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> >> --- >> arch/x86/entry/entry_32.S | 12 ++++++------ >> 1 file changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S >> index 2767c625a52c..95c94d48ecd2 100644 >> --- a/arch/x86/entry/entry_32.S >> +++ b/arch/x86/entry/entry_32.S >> @@ -389,6 +389,12 @@ >> * that register for the time this macro runs >> */ >> >> + /* >> + * Clear unused upper bits of the dword containing the word-sized CS >> + * slot in pt_regs in case hardware didn't clear it for us. >> + */ >> + andl $(0x0000ffff), PT_CS(%esp) >> + > > Please improve the comment. Since commit: > > commit 385eca8f277c4c34f361a4c3a088fd876d29ae21 > Author: Andy Lutomirski <luto@kernel.org> > Date: Fri Jul 28 06:00:30 2017 -0700 > > x86/asm/32: Make pt_regs's segment registers be 16 bits > > Those fields are genuinely 16 bit. So the comment should say > something like "Those high bits are used for CS_FROM_ENTRY_STACK and > CS_FROM_USER_CR3".
/* * The high bits of the CS dword (__csh) are used for * CS_FROM_ENTRY_STACK and CS_FROM_USER_CR3. Clear them in case * hardware didn't do this for us. */
OK? I will send out v2 with this wording soon.
> > Also, can you fold something like this in: > > diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S > index 2767c625a52c..358eed8cf62a 100644 > --- a/arch/x86/entry/entry_32.S > +++ b/arch/x86/entry/entry_32.S > @@ -171,7 +171,7 @@ > ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI > .if \no_user_check == 0 > /* coming from usermode? */ > - testl $SEGMENT_RPL_MASK, PT_CS(%esp) > + testb $SEGMENT_RPL_MASK, PT_CS(%esp) > jz .Lend_\@ > .endif > /* On user-cr3? */ >
Makes sense, but this looks like a separate patch to me.
Jan
-- Siemens AG, Corporate Technology, CT RDA IOT SES-DE Corporate Competence Center Embedded Linux
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