Hi Pingfan, On Tue, 18 Jan 2022 15:48:12 +0800 Pingfan Liu <[email protected]> wrote:
> From: Kairui Song <[email protected]> > > Since kernel commit 14c127c957c1 ('arm64: mm: Flip kernel VA space'), > the memory layout on arm64 have changed, and kexec-tools can no longer > get the the right PAGE_OFFSET based on _text symbol. > > Prior to that, the kimage (_text) lays above PAGE_END with this layout: > 0 -> VA_START : Usespace > VA_START -> VA_START + 256M : BPF JIT, Modules > VA_START + 256M -> PAGE_OFFSET - (~GB misc) : Vmalloc (KERNEL _text HERE) > PAGE_OFFSET -> ... : * Linear map * > > And here we have: > VA_START = -1UL << VA_BITS > PAGE_OFFSET = -1UL << (VA_BITS - 1) > _text < -1UL << (VA_BITS - 1) > > Kernel image lays somewhere between VA_START and PAGE_OFFSET, so we just > calc VA_BITS by getting the highest unset bit of _text symbol address, > and shift one less bit of VA_BITS to get page offset. This works as long > as KASLR don't put kernel in a too high location (which is commented inline). > > And after that commit, kernel layout have changed: > 0 -> PAGE_OFFSET : Userspace > PAGE_OFFSET -> PAGE_END : * Linear map * > PAGE_END -> PAGE_END + 128M : bpf jit region > PAGE_END + 128M -> PAGE_END + 256MB : modules > PAGE_END + 256M -> ... : vmalloc (KERNEL _text HERE) > > Here we have: > PAGE_OFFSET = -1UL << VA_BITS > PAGE_END = -1UL << (VA_BITS - 1) > _text > -1UL << (VA_BITS - 1) > > Kernel image now lays above PAGE_END, so we have to shift one more bit to > get the VA_BITS, and shift the exact VA_BITS for PAGE_OFFSET. > > We can simply check if "_text > -1UL << (VA_BITS - 1)" is true to judge > which layout is being used and shift the page offset occordingly. > > Signed-off-by: Kairui Song <[email protected]> > (rebased and stripped by Pingfan ) > Signed-off-by: Pingfan Liu <[email protected]> > Cc: Simon Horman <[email protected]> > Cc: Philipp Rudo <[email protected]> > To: [email protected] > --- > kexec/arch/arm64/kexec-arm64.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c > index 793799b..ce7a5bb 100644 > --- a/kexec/arch/arm64/kexec-arm64.c > +++ b/kexec/arch/arm64/kexec-arm64.c > @@ -923,13 +923,25 @@ out: > > int get_page_offset(unsigned long *page_offset) > { > + unsigned long long text_sym_addr, kernel_va_mid; > int ret; > > + text_sym_addr = get_kernel_sym("_text"); > + if (text_sym_addr == 0) { > + fprintf(stderr, "Can't get the symbol of _text to calculate > page_offset.\n"); > + return -1; > + } > + > ret = get_va_bits(); > if (ret < 0) > return ret; > > - if (va_bits < 52) > + /* Since kernel 5.4, kernel image is put above > + * UINT64_MAX << (va_bits - 1) > + */ > + kernel_va_mid = UINT64_MAX << (va_bits - 1); > + /* older kernel */ > + if (text_sym_addr < kernel_va_mid) > *page_offset = UINT64_MAX << (va_bits - 1); > else > *page_offset = UINT64_MAX << va_bits; I would drop the kernel_va_mid and simply use *page_offset = UINT64_MAX << (va_bits - 1) if (*page_offset > text_sym_addr > *page_offset) *page_offset = UINT64_MAX << va_bits but that's more a matter of taste. Reviewed-by: Philipp Rudo <[email protected]> _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
