Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
Hello Brian, On 01-22-16, Brian Gerst wrote: > > > > - /* Is the address not 2M aligned? */ > > - movq%rbp, %rax > > - andl$~PMD_PAGE_MASK, %eax > > - testl %eax, %eax > > - jnz bad_address > > - > > /* > > * Is the address too large? > > */ > > I think we still need to do the check, in case we came from a 64-bit > bootloader that directly jumped to startup_64. However, this check > can be simplified to: > > testl $~PMD_PAGE_MASK, %ebp > jnz bad_address Ah, ok, in this way we can't trust a bootloader. I just thought that 64-bit entry point is startup_64 from arch/x86/boot/compressed/head_64.S Thank you.
Re: [RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
On Fri, Jan 22, 2016 at 1:13 PM, Alexander Kuleshov wrote: > We check that the base address of the kernel is 2M aligned in > the arch/x86/kernel/head_65.S right after jump to the decompressed > kernel. But we already have a check in the decompress_kernel() > which validates that kernel location is MIN_KERNEL_ALIGN aligned > which is 2M too for x86_64. > > Signed-off-by: Alexander Kuleshov > --- > arch/x86/kernel/head_64.S | 6 -- > 1 file changed, 6 deletions(-) > > diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S > index ffdc0e8..4967cba 100644 > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -75,12 +75,6 @@ startup_64: > leaq_text(%rip), %rbp > subq$_text - __START_KERNEL_map, %rbp > > - /* Is the address not 2M aligned? */ > - movq%rbp, %rax > - andl$~PMD_PAGE_MASK, %eax > - testl %eax, %eax > - jnz bad_address > - > /* > * Is the address too large? > */ I think we still need to do the check, in case we came from a 64-bit bootloader that directly jumped to startup_64. However, this check can be simplified to: testl $~PMD_PAGE_MASK, %ebp jnz bad_address -- Brian Gerst
[RFC PATCH] x86/head_64.S: remove redundant check that kernel address is 2M aligned
We check that the base address of the kernel is 2M aligned in the arch/x86/kernel/head_65.S right after jump to the decompressed kernel. But we already have a check in the decompress_kernel() which validates that kernel location is MIN_KERNEL_ALIGN aligned which is 2M too for x86_64. Signed-off-by: Alexander Kuleshov --- arch/x86/kernel/head_64.S | 6 -- 1 file changed, 6 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index ffdc0e8..4967cba 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -75,12 +75,6 @@ startup_64: leaq_text(%rip), %rbp subq$_text - __START_KERNEL_map, %rbp - /* Is the address not 2M aligned? */ - movq%rbp, %rax - andl$~PMD_PAGE_MASK, %eax - testl %eax, %eax - jnz bad_address - /* * Is the address too large? */ -- 2.7.0.25.gfc10eb5
